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Book_A_c 

CopightN 0 _ 


COPYRIGHT DEPOSIT; 
















WORKS OF E. B. WILSON, E.M., 


PUBLISHED BY 

JOHN WILEY & SONS. 


Cyanide Processes. 

i2mo, cloth, $1.50. 

The Chlorination Process. 

i2mo, cloth, $1.50. 

Practical Mine Ventilation. 

For the Use of Mining Engineers, Students, and 
Practical Men. With plates. i6mo, cloth, $1.25. 

Hydraulic and Placer Mining. 

With illustrations, including full-page half-tones. 
i2mo, vi + 234 pages, cloth, $2.00. 










Ox 


PROCESSES. 



/ 


BY 


E. B. WILSON, E.M. 

< * 





THIRD EDITION , REWRITTEN. 

FIRST THOUSAND. 


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NEW YORK: 

JOHN WILEY & SONS. 

London: CHAPMAN & HALL, Limited. 

1902. 



-rH 


THE LIBRARY OF 
CONGRESS, 
Two Copies Received 

JUN. 5 1902 

Copyright entry 
i'Vw^ _ 1 ej 0 i~ 

CLASS XXc. No. 

i If 0 S’ b 

COPY B. 


Copyright, 1895, 1002, 

BY 

E. B. WILSON 



ROBERT DRUMMOND, PRINTER, NEW YORK. 


D-1 iHo / 








PREFACE. 


Owing to frequent improvements made in cyanid- 
ing, the author was compelled to rewrite his book in 
order to keep it up to date. Since the first edition of 
“Cyanide Processes,” many matters which were at 
that time mere suppositions have been worked out; a 
considerable number of points called facts have been 
disproved, hence at present the process is on a much 
more stable foundation. Wherever the process is used 
metallurgists have given their practice, and the par¬ 
ticular points they have observed or experimented upon, 
to the world, with the result that those adopting the 
process to-day have no need of working haphazard, as 
those in the past were compelled to do. 

This revision has been carried on with a view to 
meeting the requirements of men engaged in the active 
affairs of life; also for practical millmen and hydro¬ 
metallurgists, who require their information in con¬ 
densed form, free from padding and ancient history. 

Electro-cyaniding. is thoroughly discussed, for the 

iii 



IV 


PREFACE. 


author believes too little time has been devoted to this 
branch of the subject, which from a scientific stand¬ 
point presents great possibilities for economy and 
success in the recovery of gold. 

The criticisms on the former book have been 
received \vith thanks, and wherever good have been 
adopted in this volume. 

There are critics who will take exception to the 
language used in the text, as they did in the former 
volume, and accuse the author of being an ‘‘ A.cadeemic 
bantod.” To relieve their minds, it is to be under¬ 
stood that the technical writer has about eight hundred 
words to choose from, and in case he makes a promis¬ 
cuous use of four hundred of the eight hundred words, 
the average citizen will claim he writes unintelligibly. 
Our aim has been to be pedagogic rather than pedantic, 
in older to reach those who need the information as it 
is, and not as it might be put in words. 

At the end of the work will be found a list of 
patents granted in the United States for matters touch¬ 
ing upon the cyanide process. 

Particular instruction is furnished by illustrations, 
wherever the text is difficult to make clear and precise 
without them. 


May, 1902. 


E. B. Wilson. 


CONTENTS. 


PAGE 

Preface . iii 

CHAPTER I. 

Ores Suitable for Cyanide Processes . i 

CHAPTER II. 

Potassium Cyanide and Oxygen. 14 

CHAPTER III. 

Chemistry of the Process. 25 

CHAPTER IV. 

Laboratory Tests. 3$ 

CHAPTER V. 

Plants for Cyaniding. 55 

CHAPTER VI. 

Leaching the Ore. 74 

CHAPTER VII. 

Precipitating Gold from Cyanide Solutions. 86 

v 











VI 


CONTENTS. 


CHAPTER VIII. 


Treatment of Bullion 


PAGE 

118 


CHAPTER IX. 

Treatment of Concentrates and Slimes 

CHAPTER X. 

Electricity Applied to Cyaniding. 


Electrodes. 


The Current. 


CHAPTER XI. 


CHAPTER XII. 


I2 5 


J 35 


J 5i 


160 


Anodes. 


Cathodes. 


CHAPTER XIII. 


CHAPTER XIV. 


CHAPTER XV. 

Siemens-Halsxe and Pelatan-Clerici Processes. 


CHAPTER XVI. 


General Information, 
Index. 


165 


170 


175 


187 

197 












CYANIDE PROCESSES. 


CHAPTER I. 

ORES SUITABLE FOR THE CYANIDE PROCESS. 

Definitions.—Any mineral that it will pay to work is 
an ore. There are two classes of ores which contain 
gold, termed free-milling and refractory, and as they 
both enter into this discussion their character should 
be understood. 

Free-milling Ores are those which have their gold 
particles in such a condition that when liberated from 
enclosing rock they are free to alloy with mercury. 

Gold in free-milling ores is not entirely dissolved by 
mercury, in fact 60 per cent is a high recovery by 
amalgamation. 

When treating such ores the usual procedure is to 
stamp them wet, and amalgamate as much of the gold 
as possible in the mortar and on the plates outside 
the mortar. The plates are either of copper coated 



2 


CYANIDE PROCESSES. 


with quicksilver, or else are copper plates silver- 
plated and then coated with quicksilver. They are 
given a fairly good slope to allow the pulp to flow over 
and from their surfaces freely. The gold not caught 
in the mortar or on the plates will be lost if the tailings 
are allowed to waste, therefore at well-regulated mills 
they are impounded in settling-dams or other con¬ 
trivances which will allow them to settle from the 
water holding them in supension; or they are led 
direct to the cyanide vats; or still another process, that 
of concentration, may be practised. 

Some of the reasons advanced to account for the 
comparatively small recovery of gold from free-milling 
ores are: (a) that the particles are so small and light 
that they float away; ( b ) that the particles are covered 
with a film of clay, grease, or sulphur; (c) that the gold 
is rusty, tarnished, or covered with a film of oxide. 
Whatever the cause at any particular mill, those por¬ 
tions of the gold which are not recovered are virtually 
refractory as far as amalgamation is concerned. 

Refractory Ores. —Those ores which are not free- 
milling, and whose gold refuses to alloy with mercury 
in the mortar or on the plates, are refractory. Many 
ores which are free-milling at the surface become 
refractory as soon as water-level is reached and the 
atmospheric agencies cannot readily affect or, as it is 
called, oxidize them. Such ores may sometimes be 


ORES SUITABLE FOR THE CYANIDE PROCESS. 


3 


effectually treated by cyaniding after preliminary 
treatment. Ores containing sulphides, tellurides, 
arsenides, bismuth, selenium, and possibly some other 
metalloids are in the refractory class. 

The usual method of treatment for such ores if they 
are to be lixiviated is to crush in a rock-breaker, dry 
in a furnace, pulverize by rolls or stamps, roast to 
drive off the volatile substances and oxidize the base 
metals, and then leach in tanks. 

Concentrates.—Those portions of ores which have 
been treated in the stamp-mill and proved refractory 
may contain sulphides which enclose gold. The sul¬ 
phides, being of greater specific gravity than thegangue, 
can be separated from it and the valuable portion of 
the ore thus reduced in bulk. Concentration of this 
description depends upon the difference in weight 
between the valuable and worthless minerals, and is 
accomplished by gigs, hydraulic classifiers, and bump¬ 
ing-tables. 

Sulphides may be concentrated direct from ores 
without preliminary treatment, and such is the usual 
practice with refractory ores. The operation of con¬ 
centrating sulphides will not differ from that for 
tailings. 

Tailings.—That portion of ore remaining after amal¬ 
gamation is termed the tailings. At some operations 
these may be worked profitably by the cyanide process. 


4 


CYANIDE PROCESSES. 


In South Africa the ore treated by cyaniding belongs 
to this class. Tailings which contain $3 in gold can 
sometimes be worked at a profit by this process, since 
as high as 90 per cent of the gold can sometimes be 
extracted. Since ore must be stamped for amalgama¬ 
tion, the treatment of tailings can be accomplished for 
simply the cost of handling and chemicals. There is 
often considerable gold in tailings half amalgamated 
that is covered with mercury but not alloyed; such 
gold is not attacked by cyanide and will not be recov¬ 
ered until the mercury is removed. Fortunately the 
quantity of gold in such a state is not large. Amalgam 
is sometimes scoured from the plates and gets into 
the tailings; this also is sometimes a loss, for cyanide 
will not attack the amalgam readily. 

Slimes. Considerable ore becomes impalpable dur¬ 
ing crushing, and this mixed with water floats away as 
slime, which at times carries a large portion of the 
gold; hence it is important that the water containing 
such fine material should be led to settling-tanks or 
ponds. When settling-tanks are employed the stuff 
would not settle for days unless some artificial means 
were adopted to hasten the operation. It has been 
found that the addition of a little lime, soap, or alum 
will precipitate the slimes in a short time. Too much 
lime should not be added; but this is a matter to be 
determined by experiment, and not one for which a 


ORES SUITABLE FOR THE CYANIDE PROCESS. 5 

rule can be formulated. Fine slimes are unavoidable, 
and in the case of clayey or oxidized ores may be in 
such quantities as to prevent percolation unless washed 
off and treated separately. 

Some idea of the quantity of fine ore which is made 
in stamping - may be obtained from an examination of 
the following data, which are the results of stamping 
through 30-, 40-, and 60-mesh screens. 

Stamping to 30-mesh screen: 

20 per cent remained on a 90-mesh screen. 

18 “ ** “ “60 “ ** 

13 “ “ “ “ 40 “ “ 

Stamping to 40-mesh screen: 

22 per cent remained on a 90-mesh screen. 

12“ “ “ “ 60 “ “ 

Stamping to 60-mesh screen: 

18 per cent remained on a 90-mesh screen; the 
remainder of the pulp passed through. 

When it is considered that there are 8100 holes in a 
square inch of 90-mesh screen, and that only 18 per 
cent of the product would remain on the screen when 
stamping to a 60-mesh screen, some idea of the fine¬ 
ness of the material which passes through may be 
obtained. 

Mr. E. G. Banks experimented to ascertain the 
relative values of the different finenesses of ore crushed 
to pass a 30-mesh screen: 


6 


CYANIDE PROCESSES . 


Per Ton. 

2 -16# remained on 40-mesh screen. Value $19.70 

9 * 2 9 $ “ “ 60 “ “ “ $17.80 

2$.72% “ “ 80 ** “ <* $22.50 

74.28$ passed through 80 “ “ «« $26.75 

Sulphide ores are brittle and should not be pul¬ 
verized fine when it can be avoided. Such ores are 
readily converted into slimes by crushing - with 
rolls. 

Dry stamping and crushing cause more slimes than 
wet stamping. 

The stamps falling on the ore drive the crushed 
particles up against the screens and, there being no 
water present to carry them through, they fall back 
into the mortar and possibly again go under the 
stamp, to be further pulverized. Dry stamping can be 
carried on almost as expeditiously as wet stamping. 
However the results are as described, and the system 
is not practised where it can be avoided. 

When crushing with rolls the ore is first dried as in 
the case of crushing dry with stamps, but there is this 
redeeming feature, there are not so many slimes made. 

Gold and Silver are each dissolved by potassic 
cyanide under certain conditions. The action upon 
coarse gold is slow, therefore in such cases amalgama¬ 
tion should precede cyaniding. 

Silver in the form of chloride is readily attacked by 


ORES SUITABLE FOR THE CYANIDE PROCESS. 7 

potassium cyanide solutions, while other silver ores 
with the exception of subsulphide Ag 2 S are not. 

Degree of Fineness.—In every class of metallurgical 
work uniformity in the size of product is desirable, but 
as this seems an impossibility, owing to the fine ore 
made during crushing operations, cyaniding is some¬ 
times impracticable. However it may be taken for 
granted that the best results will be obtained when the 
product is uniform. 

The degree of fineness required will depend upon 
the ore, that is, upon the manner in which the metal 
is encased in the ore. Porous ores will not need the 
same degree of fineness as hard compact ores, for in 
the former case the solutions can penetrate the ore and 
get to the metal, while they cannot in the latter. 

An open porous ore might not need finer crushing 
than \ inch, while a compact ore might require pul¬ 
verizing to pass a 6o-mesh screen. 

Besides the avoidance of slimes when coarse crush¬ 
ing can be practised, there are other features which 
commend it, such as time saved in crushing, increased 
product from the stamps, decrease in the quantity of 
water required, and time saved in subsequent drainage. 
On the other hand, coarse crushing requires that the 
solutions be left longer in contact with the ore. 

Whenever ores must be crushed fine, the water 
drains slowly from them and they pack. This is par- 


8 


CYANIDE PROCESSES . 


ticularly the case with clayey or slimy ores. When 
drainage will not exceed £ inch per hour, treatment by 
lixiviation is impracticable. The average speed of 
drainage should be at least 12 inches per hour inde¬ 
pendent of mechanical arrangements. If drainage 
does not come up to or exceed these figures, the slimes 
must be washed from the ore. In some cases it may 

be found advantageous to mix sand with the ore to 
increase percolation. 

Acid Ores.—Certain ores which have been partially 
oxidized, such as sulphides, will, when placed in 
water, permit metallic salts to be dissolved from them. 
These metallic salts, if acid, will destroy cyanide and 
increase the cost of that chemical for the operation, 
besides lessening the recovery of gold. Such ores 
may sometimes be freed of acidity by a preliminary 
wash of water, or be neutralized by the addition of 
an alkali, such as calcium oxide or sodium hydrate. 

Base-metal Ores.—The base-metal ores are those 
containing antimony, iron, copper, lead, manganese, 
and zinc. Cyanide of potassium dissolves metals more 
or less, generally forming double salts. The affinity 
of cyanogen for gold rather than the other base metals, 
with the exception possibly of copper, is such that the 
weaker the solution of cyanide is, the less likely are 
the base metals to be attacked. Copper compounds 
physically hard are not acted upon, but when soft and 


ORES SUITABLE FOR THE CYANIDE PROCESS . 9 

porous copper ores are in the solution they interfere 
with the process. 

Copper carbonate ores have so marked a reaction 
upon cyanide solutions that it is necessary before 
treatment to subject them to either a calcining roast or 
to sulphuric acid treatment. 

Dr. Scheidel found that 8 grams of a copper car¬ 
bonate ore reduced the cyanide from 2.73 per cent to 
.05 per cent in fifteen minutes. Where such strong 
solutions are employed in tests, it is found that the 
gold is extracted quickly. In the case just cited 70 
per cent of the gold was extracted, bearing out the 
former statement that weak solutions attack gold in 
preference to base metals. It is during the treatment 
of cupriferous ores that the selective action of weak 
cyanide solutions for gold becomes most apparent. 
An ore containing sufficient copper to decompose a 
1 per cent cyanide solution would have a very much 
less pffect upon a solution containing 0.25 per cent. 

Antimony ores are under some conditions affected 
by potassic cyanide. This is true of stibnite or sul¬ 
phide of antimony, which forms sulphide of potassium 
and sulphocyanogcn. Such ores arc very compact and 
require very fine crushing to avoid an excessive use of 
potassic cyanide. 

Bismuth is said to act in the same manner as copper 
and antimony. 


IO 


CYANIDE PROCESSES. 


Sulphide Ores.—Clean, fresh pyrites are not acted 
upon by weak cyanide solutions, although it has been 
noted that the decomposition products of this mineral, 
such as iron sulphates, have a destructive effect. 
Copper pyrites are oxidized to a soluble sulphate at 
low temperatures, and this salt requires a greater heat 
, to decompose it than iron sulphate. 

Galena, or sulphide of lead, is slowly attacked by 
cyanides, but all its sulphur combines with cyanogen 
to form sulphocyanogen, while the lead comes into the 
solution as a hydrate. 

Zinc-blende, or sulphide of zinc, is scarcely effected 
by cyanide more than pyrite, FeS 2 . Zinc carbonate 
will act like any other base metal oxide and must be 
calcined. 

Alkaline Sulphides, when formed in any manner 
during cyaniding, will cause a loss of gold, by precipi¬ 
tating it and coating it with a film of sulphur, thus 
preventing the solution from redissolving. If the 
chemist can invent some method of making the sulphur, 
forming antimony and copper sulphides unite with the 
cyanogen rather than the potassium, and thus prevent 
the formation of alkaline sulphides which precipitate 
and hold back the gold from solution, such ores could 
be treated as readily as the other sulphides. As it is, 
there seems to be some peculiarity in the sulphur of 
antimony and copper sulphides which allows them to 


ORES SUITABLE FOR THE CYANIDE PROCESS. 11 

be attacked readily by potassic cyanide, forming' the 
objectionable salt potassic sulphide, • Iv.,S. It is pre¬ 
sumed that, owing to the readily oxidizable nature of 
these two metallic sulphides, they are converted into 
sulphates and as such act upon the cyanide. 

Tellurium.—Ores containing tellurium, such as petz- 
ite and calverite, do not seem to have a bad effect 
upon potassic cyanide solutions, while tellurium oxide 
is stated to be insoluble in cyanides. Tellurium ores 
are compact and require fine crushing; even then the 
action of the solution is slow. 

It is customary to roast Cripple Creek, Colorado, 
ores in order to make them more porous and thus 
increase'the rate of percolation, and at the same time 
leaching can be effected sooner. Experiments show 
that tellurium is soluble in the presence of sodium 
dioxide. 

Arsenical Ores, such as those at Mercur, Utah, do 
not seem to greatly interfere with the cyanide opera¬ 
tions at that place, since the largest plants in the 
United States are erected there. The ore is porous 
and readily permits the solutions to percolate, so that 
pieces -J inch in diameter are sucessfully leached. 
Carbonaceous shales and sulphur seem to be the only 
materials that give trouble at Mercur. Cinnabar is 
quite abundant, but nothing is given out concerning its 
being injurious to the process, while its presence is 


I 2 


CYANIDE PROCESSES. 


considered to be a good indication of gold. Cyanide 
seems to attack cinnabar, for when roasting the gold 
precipitates the men become salivated by the fumes 
unless careful. 

Manganese does not seem to have much effect upon 
cyanide solutions, while 

Cobalt and Nickel have a decided effect upon the 

i 

consumption of cyanide, acting similarly to copper. 

Roasting Ores.—In all probability if a dead roast is 
to be given to oxidize base-metal salts, the chlorination 
process will prove as economical in operation as 
cyaniding, provided no lime or magnesium is in the 
ore. There are, however, ores which do not need an 
oxidizing roast but merely a dehydrating roast to make 
them porous. Such roasting or calcining should not 
exceed a temperature of 300° F., otherwise they might 
sinter, especially if lime or magnesia were present. 
Leaching would possibly in such cases be retarded by 
the formation of hydraulic cement. Ores which are to 
be crushed dry must be given a dehydrating roast, 
otherwise they will clog the screens and not be sized 
properly; if, therefore, they are made more porous at 
the same time that they are being dehydrated, so much 
the better for the process. Dehydrating roast will 
not answer for chlorination; that process requires a 
thorough oxidizing and chloridizing roast. Some sul¬ 
phides will not interfere with the cyanide process, but 


ORES SUITABLE FOR THE CYANIDE PROCESS. 13 

it is possible that the heat for dehydrating may con¬ 
vert sulphides with the aid of moisture present into 
sulphates. This is especially important in the case of 
copper pyrite, since it seems to be the result of heat 
and moisture that converts them into the peculiar sul¬ 
phates described. 

The scope of the cyanide process can only be deter¬ 
mined by experiment, for in one case the percentage 
of extraction will be high, while in another, with Con¬ 
ditions almost similar, it will be low. To ascertain 
the fitness of an ore for the process, leaching tests 
should be made first in the laboratory and then on a 
larger scale. 


CHAPTER II. 

POTASSIUM CYANIDE AND OXYGEN. 

Eisner’s Equation.—That gold was soluble in cyanide 
of potassium solutions was known to Hagen in 1806. 
L. Eisner stated in 1844 that gold and silver could be 
dissolved in potassium cyanide without decomposition 
of water. He further stated that the dissolution of the 
metals was the consequence of the action of oxygen, 
which, absorbed from the air, decomposed part of the 
cyanide, thus forming a double salt, auro-potassic 
cyanide, which has later been stated in the following 
equation, known as “Eisner’s Equation 

2Au -f 4KCy + O -f H 2 0 = 2AuKCy., -f 2KOH. 

The first scientific literature on the subject is by 
Prince Bagration in 1843. He concluded his paper 
u ith the remark that in the future cyanide of potassium 
must be enumerated among the solvents of gold. 
I-araday made use of a cyanide solution to produce 
thin films of gold in 1857. Ten years later J. H. Rae 
took out the first patent for applying cyanide to obtain 


14 


POTASSIUM CYANIDE AND OXYGEN. 


*5 


gold from the ores direct. He was followed by 
Faucett in 1881 ; he in turn by Sanders in 1881; then 
by J. W. Simpson in 1885; finally by MacArthur and 
Forrest in 1889. 

Patents. —An examination of the patents granted for 
cyanide processes and improvements shows that it is 
an easy matter to obtain a patent, but a difficult matter 
to retain it if some one else wants to make use of 
anything claimed in the patent. The inventions for 
this process have been many, but the improvements 
few. 

The MacArthur-Forrest patents are not valid except 
in so far as they apply to the precipitation of gold from 
cyanide solutions by zinc filaments. 

The zinc-fume precipitation process has been decided 
against the owner of the patent. 

The precipitation of gold from solutions by charcoal 
was in use long before Johnson’s patent. 

What is now termed the pneumatic cyanide process 
was not considered worth patenting by the author, 
although it was undoubtedly originated in this country 
as soon as in New Zealand. 

Oxygen and Cyanide. —Eisner’s equation at one time 
caused much comment, but it has now been satisfac¬ 
torily settled that oxygen plays an important role in 
the process. A pure solution of potassic cyanide will 
not dissolve gold to any great extent when the latter 


10 CYANIDE PROCESSES. 

is immersed in it, but dissolves it readily when oxygen 
is present. For example, if gold-leaf is placed on the 
surface of a cyanide solution, it will dissolve in a few 
minutes, and the stronger the solution the quicker it 
dissolves; however, if submerged in the solution it 
dissolves but slowly, the strength of the solution affect¬ 
ing its rate of dissolution but slightly. 

MacLaurin of New Zealand in his experiments used 
gold-leaf of uniform thickness, and his deduction 
was that oxygen was necessary for the solution if 
cyanide was to dissolve gold with any rapidity. A 
piece of gold-leaf placed in a stoppered bottle lost 
O-18 per cent of its weight in ninety-two hours. 

Another piece placed in an open bottle lost 9.1 per 
cent of its weight in sixty-two hours. Still another 
piece placed in a bottle with oxygen lost 24.2 per cent 
of its weight in ninety-six hours. The strength of the 
solutions was identical in every instance. 

Experiments were made by the State Mining Bureau 
of California with dilute cyanide solutions upon metal¬ 
lic gold. 

With a 1 per cent solution it was found possible to 
dissolve such gold-leaf as is used by sign-painters in 
one hour. When dentists’ foil was used, about six 
times thicker than painters’ foil, it required forty-eight 
hours to dissolve. 

Mr. J. B. Hanney verified Eisner’s equation and 


POTASSIUM CYANIDE AND OXYGEN. 17 

MacLaurin’s experiments in a practical way. His 
theory was that dilute cyanide solutions acted more 
rapidly on gold. He attributed this to the cyanide 
displacing oxygen by dissolving in the water, and that 
therefore gold could not dissolve until oxygen had 
been absorbed from the air. To carry out this theory 
he treated ores with dilute and then with strong solu¬ 
tion. 

He found that the rate of dissolution of gold in¬ 
creased with the strength of the solution, provided 
oxygen of the air could come in contact with the 
gold. 

Mr. Hanney invented an electro-chemical apparatus 
which he used in his experiments. In direct opposi¬ 
tion to this Mr. Miller has patented an apparatus to 
keep the air away from the solution. 

From MacLaurin’s experiments the following is 
deduced: 

1. That oxygen is necessary for dissolving gold in 
a cyanide soultion, and that it combines with the 
potassium of the potassium cyanide in the proportion 
required by Eisner’s equation. 

2 . The rate at which gold is dissolved in a solution 
of potassium cyanide passes through its maximum in 
passing from dilute to concentrated solution, due to 
the fact that the solubility of oxygen in a cyanide solu¬ 
tion decreases with the concentration. 


18 


CYANIDE PROCESSES . 


Vaiious ideas have been advanced in order to hasten 
the solution of gold in cyanide solutions, most of them 
depending upon increasing the quantity of oxygen. 
Agitation has been employed with this end in view, 
but, owing to an excessive increase in the quantity of 

cyanide, it has not been widely adopted, except for 
slimes. 

Several forms of agitators, such as paddles to stir up 
the ore and solution, drawing off the solution and 
rushing it back in again from the bottom of the vat, 
circulating the pulp by centrifugal pumps, and pneu¬ 
matic agitation, have been employed with more or less 
success. 

There is no question but that agitation quickens the 
leaching process, but it may be surmised from its slow 

introduction that the added cost necessary for power is 
a drawback. 

Agitation may in some cases be economical in prac¬ 
tice, and there are no doubt many instances where by 
agitation triple the quantity of ore can be leached in a 
given time at the same total cost. 

One item in favor of agitation is the speed with 
which tanks can be discharged where proper arrange¬ 
ments have been perfected for the purpose. 

Agitation at present finds its greatest employment 

in treating slimes and ore which cannot be percolated 
in regular cyaniding. 


POTASSIUM CYANIDE AND OXYGEN . 19 

Chemicals for Oxidation. —For the purpose of hasten¬ 
ing the leaching operation several inventors have 
worked along the lines of furnishing oxidizing agents 
of a chemical nature to replace the oxygen of the air. 

Several chemicals are capable of liberating nascent 
cyanogen in a cyanide solution, particularly potassic 
chlorate, nitrate, permanganate, bichromate, and the 
peroxides of barium, manganese, lead, and sodium. 
Besides these the haloids iodine and bromine act in a 
vigorous manner. All of these compounds act as 
oxidizing agents when added to a potassium cyanide 
solution, and increase the solubility of gold, some by 
adding oxygen and others by taking the place of 
oxygen. Among the most convenient is peroxide of 
sodium and peroxide of hydrogen. In 1893 J. C. 
Montgomerie obtained patents for the use of sodium 
peroxide, sodium oxide, and sodium hydrate as oxidiz¬ 
ing agents, although experiments were made by Prof. 
Christy in 1892-3 with the same oxidizing agents. 

Cyanogen Bromide. — Experiments made by Prof. 
Christy in 1894 showed that if cyanogen bromide was 
added to a solution of potassium cyanide, potassium 
bromide was formed and cyanogen liberated as 
follows: 


BrCN + KCN = KBr + 2CN. 

In the presence of metallic gold and in an excess of 


20 


CYANIDE PROCESSES. 


potassium cyanide the double salt auro-potassic cyanide 
was formed, and potassium bromide as well: 

3KCN 4- 2Au -f BrCN = 2 KAuCN., 4- KBr. 

Messrs. Sulman and Teed claim to have made the 
first discovery of this reagent, and in fact received an 
English patent in 1895. A. W. Warwick, E. A. 
Schneider, and yet another make the same claims 
about the same time, but probably Prof. Christy’s 
experiments antedate them all. 

A simpler process, such as the use of bromine-water, 

was next tried. The reactions were analyzed as 
follows: 

2KCN + Br -f Au = KAuCN,, -f- KBr. 

To use bromine in either case requires experience 
and skill, otherwise a great loss of cyanogen will 
occur and poor results follow. The reason given for 
this is that free cyanogen has a tendency to oxidize 
into certain impure compounds; consequently if 
cyanogen is set free faster than the gold can reach it 
a loss of cyanogen occurs. Strong solutions of bromine 
and cyanide of potassium should be avoided, for if there 
is no contact with gold when cyanogen is set free there 
will be a decided loss. It not being possible in 
ordmary hxiviation to have the gold in intimate con¬ 
tact with cyanogen continually, there must inevitably 
be a loss of cyanogen which will mitigate against the 


POTASSIUM CYANIDE AND OXYGEN. 


21 


use of bromine, although the combined use of KCN 
and Br will dissolve four times as much gold in a given 
time. A further drawback to the use of the mixture 
is the increased cost of the solution and the loss of 
chemicals. 

Chlorine-water.—Chlorine-water may be used instead 
of bromine-water. 

This might suggest itself, as chlorine is one of the 
haloid salts. 

According to theoretical deductions, 
r ounce of bromine should dissolve 2.45 ounces of gold 

1 “ “chlorine “ “ 5.52 “ “ “ 

1 “ “ oxygen “ “ 24.5 “ “ “ 

The bromine process has been in practical operation, 
performing the leaching operation in fifteen hours, with 
a consumption of 4 ounces KCN and 1.75 ounces 
BrCN. The percentage of extraction is said to be 
about 90. 

Considerable criticism of this process has been 
indulged in by people interested in other processes, 
but it may in the future demonstrate its usefulness. 

Iodine.—The reaction which occurs in case iodine is 
employed in a potassic cyanide solution to hasten the 
solution of gold may Be stated as follows: 

2KCN + Au + I = KAuCN 2 + KI. 

The results and deductions obtained are somewhat 


22 


CYANIDE PROCESSES. 


similar to those mentioned above and need not be 
repeated. 

On the whole the extra cost of treatment and the 
loss of cyanogen have been such that atmospheric 
oxygen is employed wherever possible. 

hrom what has been said it is evident that without 
oxygen or an oxidizing agent potassium cyanide has 
absolutely no action upon gold, and that if sufficient 
oxygen is not present it must be supplied artificially. 
In some instances the entire solution is drawn off that 
the air may follow the solution down through the ore, 
but it will not be policy to aerate the cyanide solutions 
unless in contact with the ore, on account of a Joss of 
cyanogen which will result. 

Iheie is danger in using too much oxidizer, as 
secondary reactions will probably occur, especially if 
the ores contain sulphides, arsenides, atimonides, and 
lead; for if free cyanogen is liberated faster than it can 
come in contact with the gold, it will run down into 
oxidized products without doing any good. 

This is one reason why without care and expert 
supervision the cyanide process is not as successful as 
it should be with low-grade ores. 

It seems to be the free cyanogen only that attacks 
gold, and if potassic cyanide is in excess, paracyanogen 
is formed which absorbs oxygen and prevents cyanogen 
from attacking the gold. This is better illustrated by 



POTASSIUM CYANIDE AND OXYGEN. 


2 3 


stating that while the time occupied by extraction will 
be less for a strong solution, the consumption of cyanide 
will be more than if a weak solution were used. 

Yet this does not always hold good, as the following 
experiments will show: 

(i) KCN solution before experiment 1.0809 P er cent 
KCN “ after “ 0.5145 “ 

Loss of KCN.0.5664 per cent 

Extraction in 15 hours; Au, 0.5 mg.; Ag, 72.45 mg. 

(2) KCN solution before experiment 0.5404 per cent 

KCN “ after “ 0.0837 “ 

Loss of KCN.0.4567 per cent 

Extraction in 15 hours; Au, 2.3 mg. ; Ag, 138.4 mg. 

(3) KCN solution before experiment o. 1081 per cent 

KCN “ after “ 0.0042 “ 

Loss of KCN.o. 1039 P er cent 

Extraction in 15 hours; Au, 2.2 mg. ; Ag, 103.3 mg- 

It will be noted that with the weaker solutions the 
percentage of gold and silver extracted was more than 
with the strong solution; it is advisable, therefore, to 
test ores to ascertain the weakest cyanide solution that 
will extract the most gold from a given ore with the 
least loss of cyanide. 

Experiments made with sodium peroxide and 
hydrogen peroxide in potassium cyanide solutions, and 








2 4 


CYANIDE PROCESSES. 


with potassium cyanide clear, may be interesting at this 
time, as illustrative of their various capacities for dis¬ 
solving gold and silver. The experiments were made 
on Cripple Creek telluride ores. Time of leaching, 
40 hours. 

0.5 per cent KCN solution dissolved .36 mg. Au 
from 0.76 mg. Au. 

0.5 per cent KCN -|- 1.16 gm. N 2 0 2 dissolved .66 
mg. Au from .76 mg. Au. 

°-5 P er cent KCN -j- 10 c.c. H 2 0 2 dissolved .51 
mg. Au from .76 mg. Au. 

10 c.c. H 2 0 2 = ui 6 gm. N 2 0 2 = 0.238 available 
oxygen. 

Further experiments made with such oxidizing- 

b 

agents as potassic permanganate and bleaching- 
powder were not successful. 



CHAPTER III. 


CHEMISTRY OF THE OPERATION. 

Chemical Processes. —Cyanide lixiviation has but one 
competitor, chlorination, but both processes are not 
always adapted to the same ores, so that in many cases 
they have distinctive fields for exploiting. It was 
formerly thought that a rough laboratory test upon a few 
pounds of ore would be sufficient to determine whether 
an ore could be successfully treated by cyaniding. 
This test is not now considered sufficient, but should 
be supplemented by a five-ton test at least, for several 
ores which have given excellent extraction by labora¬ 
tory tests have failed utterly when larger quantities 
were treated. This was not due to the chemist, but to 
the ores, which probably were picked samples. It is a 
fairly well-known fact that an interested party cannot 
sample his ore properly, neither can he send proper 
samples to a testing-mill, it would seem, for nine times 
out of ten he will send picked or average samples 
when he should send run-of-mine ore, asdt is usually 

in the latter that the trouble will be found. Tail- 

25 


2 6 


CYANIDE PROCESSES. 


ings aie of course not included in the above remarks, 
d he scope of a chemical process for gold treatment is 
limited, and while it may answer admirably so long as 
certain minerals are absent, it may not work at all if 
they be present; for which reason it is advisable to 
have all the minerals in the ore likely to be encountered 
in ordinary mill working, rather than have extra quan¬ 
tities of gold in the samples. If, under such condi¬ 
tions, the chemist’s deductions are favorable, one can 
depend upon the success of the cyanide treatment 
from his tests. After the ore has been established as 
fit for the process, there is little danger of its proving 
unsatisfactory, unless the ore changes materially. 

The value of any process depends upon the profits 
obtained—another matter which should be considered 
thoroughly before the process is adopted. 

The writer is more conservative at this time than 
when he first wrote on the subject, for he has noticed 
that Mr. Paul’s statement is not to be relied upon in 
all cases, viz., “ that if laboratory tests were satisfac¬ 
tory on 50 pounds of ore, he would not hesitate to 

build a mill on that test, so uniform are the results 
obtained. ’ ’ 

The chemical reaction of the cyanide process ls 
such that after the chemist has determined the propor¬ 
tions of chemicals to be used in the treatment of any 
particular ore that has proved to be susceptible of 




CHEMISTRY OF THE OPERATION. 27 

cyamding, the work becomes practically mechanical. 
This statement has been criticised, nevertheless there 
are men working the cyanide process successfully who 

know little of its chemistry and no other chemistry 
at all. 

Eisner’s Equation.—The chemical reaction expressed 
by Eisner’s equation for gold is 

2Au + 4KCN + O + H 2 0 = 2AuKCN 2 + 2KOH. 
For silver it is 

2 Ag + 4 KCN + O + H 2 0 = 2AgKCN 2 + 2KOH. 

The equations show that double salts are formed: 
the gold salt termed aurio-potassic cyanide, the silver 
salt argentic-potassic cyanide, and also another prod¬ 
uct of the reaction, termed potassic hydrate or caustic 
potash. The double salts are quite stable, that is, are 
not easily decomposed; in fact, it is hardly possible to 
accomplish their dissolution without using a highly 
electro-positive metal or its equivalent. For that 
reason zinc in some form or an electric current seems 
best adapted to the purpose. 

In case the salts are broken up the cyanogen will 
immediately unite with the potassium of the potassic 
hydrate if a molecule is near and potassium cyanide be 
regenerated, otherwise the liberated cyanogen will 
form zinc-potassic cyanide or some paracyanogen and 
a loss occur. 


28 


CYANIDE PROCESSES. 


Cyanicides.—The term cyanicides includes all those 
agents which are destructive to cyanogen so far as they 
interfere with the extraction of gold, and also those 
agents which unite with the potassium and prevent the 
regeneration of potassium cyanide. 

The cyanicides are usually base-metal salts forming 
mineral acids, but there are other factors, such as 
decomposition due to carbon dioxide, or to those 
portions of the ore soluble in cyanide solutions. 

Acid Ores.—Ores containing partially oxidized sul¬ 
phides are destructive to cyanide, for which reason 
they must be entirely oxidized by roasting or have 
their mineral acids removed by washing if possible. 
If this is not feasible, the salts must be neutralized by 
some alkali. 

It has been stated that clean iron pyrite is not 
injurious to ICON, but it is to be understood that sul¬ 
phide ores or concentrates exposed to the weather will 
oxidize quickly and become sulphates. When such ores 
come in contact with cyanide, taking pyrite, FeS,, as an 
illustration, the following reactions undoubtedly occur: 

FeS 2 + H 2 0 + 70 = FeS 0 4 + H 2 S 0 4 . 

The acid formed must be washed from the ore 
whenever it occurs free, otherwise free hydrocyanic 
acid will be liberated and probably lost. Thus: 

H 2 S 0 4 + 2KCN = 2HCN -f K 2 S 0 4 . 

In case the acid is not washed out there is a possi- 



CHEMISTRY OF THE OPERATION. 


2 9 


bility that the free hydrocyanic acid may attack the 
gold and assist the leaching. Undoubtedly this 
would be the case if there were plenty of gold and 
nothing else attractive to prussic acid, but gold parti¬ 
cles in ore are few and far between, and the chances 
are very much against their being dissolved by the 
acid. There are instances where the mineral acids are 
actually a great help to the process; for instance, where 
the fine gold is covered with an oxide which prevents 
its absorption by cyanide. 

In such cases the mineral acid will free the gold and 
form metallic salts which would act as a cyanicide if 
not neutralized or washed away. Take for illustration 

FeS 0 4 + 2KCN = FeCN 2 + K 2 S 0 4 . 

Were lime added to neutralize the acid salt before the 
potassium.cyanide was admitted to the ore the follow¬ 
ing reaction would occur and render the salt harmless, 
thus: 

FeS 0 4 + CaO = FeO + CaS 0 4 . 

Ferrous oxide is a powerful base and would neu¬ 
tralize acid ; on the other hand it also absorbs oxygen 
readily and might pass into ferric oxide, thus: 

2 FeO + O = Fe 2 0 3 . 

This is a feeble base and would have little effect; 
besides in all probability it would be carried off in the 
water used to wash away the calcium sulphate. 


3° 


CYANIDE PROCESSES. 


If the ferric oxide is not carried off, it will combine 
with the cyanide to a greater or less extent, but seems 
to have no very serious action. 

While ferrous salts, soluble or insoluble, exist in the 
ore, lime or soda will combine with the acid to deposit 
ferric oxide. Ferrous sulphate could also form an 
insoluble basic sulphate. 

Berzelius gives the reaction between ferrous sulphate 
and oxygen as follows: 

2 FeS 0 4 + O = Fe 2 0,,2S0 3 , 

thus forming an insoluble basic sulphate. 

The reactions of the sulphates of alumina and mag¬ 
nesia are practically the same as ferrous sulphate with 

cyanide, the free prussic acid being a loss in most in- 
stances. 

Ferro and Ferri Cyanides—The reaction of ferrous 
salts with potassic cyanide is given as follows: 

FeS 0 4 + 6KCN = K 4 FeCN 6 + K 2 S 0 4 ; 

3 K 4 FeCN 4 + 6 Fe 2 S 0 4 + 3 0 = Fe 2 0 J +6K 2 S0 4 +Fe 7 CN lr 

The potassium ferro-cyanide of the first reaction is 
converted into ferri-ferro cyanide or Prussian blue. 
This is the case only when the ferric salt is in excess; 
when there is a similar mixture with the ferrous salt in 
excess Turnbull s blue is formed, thus: 

i 2 KCN+ 3 FeS 0 4 -f Fe 2 (S 0 4 ) 3 = 6 K 2 S 0 4 +Fe 3 .Fe 2 CN 

“ 12 


CHEMISTRY OF THE OPERATION. 31 

The reactions between the iron compounds and 
potassium cyanide are very complicated, and besides 
they are not fully understood, yet it is known that the 
reactions above take place and that a considerable 
cyanide loss occurs through them. If metallic iron be 
present in solutions of cyanide with gold, there will be 
no loss of cyanide due to its presence, a matter which 
permits of the use of iron tanks; but the tank iron will 
be more or less corroded and for that reason should 
be well coated with preservative, like paraffine paint. 
As an illustration take the following possible equation: 

6AuKCN 2 + 6KOH -f 2 Fe + 3 H 2 0 

= 6AuKCN + 6HCN + 6KOH + F 2 O s . 

In this equation the free prussic acid would combine 
at once with the free alkali to form potassium cyanide: 

6HCN + 6KOH + Fe 2 O s = 6KCN + 6 H 2 0 + Fe 2 0 3 . 

The first reaction shows that it is possible, if a metal 
is present, to regenerate potassium cyanide, and this 
actually occurs in zinc precipitation. 

/ 

Carbon Dioxide.—The reaction of carbon dioxide on 

potassium cyanide is as follows: 

2KCN + C 0 2 + H 2 0 = K 2 C 0 3 + 2HCN. 

The sources from which carbon dioxide may come to 
affect the solution are the atmosphere, carbonate ores, 
charcoal, or other organic matter. The prussic acid 


3 2 


CYAN I DR PROCESSES. 


set ficc according to the reaction would unite with 
whatever cyanicide w^as adjacent to its molecules. 

Charcoal.—It has -been long known that charcoal 
would precipitate gold from cyanide solutions, but the 
reaction is somewhat doubtful if it be not due to the 
carbon dioxide in the charcoal. 

Charcoal, after some hours’ contact, causes a loss of 
cyanogen by setting free prussic acid, possibly accord¬ 
ing to the following reaction: 

AuKCN 2 + C 0 2 + Ii 2 0 =3 All + KCO s + 2HCN. 

Parks found that very long contact was required for 
complete precipitation of gold from cyanide solutions. 
In New Zealand, where the ore was kiln-dried, con¬ 
siderable loss of cyanide occurred from charcoal getting 
into the ore and hence into the solutions. 

Consumption of Cyanide.—According to Eisner’s 
equation i pound of potassium cyanide should dissolve 
about 1.5 pounds of gold, but this is not approached 
in practice, the rule being that it takes between thirty 
and forty times that quantity. The loss is due to 
cyanicides, and is dependent chiefly upon the character 
of the ore and its associate minerals, but there is a 
certain quantity lost in the zinc-boxes and wash-water, 
also some is left in the tailings due to capillarity. It 
is presumed that fine ore will retain more cyanide 
solution than coarse ore, but this may be questioned, 




CHEMISTRY OF THE OPERATION. 


33 


for coarse ore in most cases requires a longer time for 
the solution to enter its pores, and it will require a 
longer time for it to come out. Again, capillarity and 
the weight of the liquor assists in forcing the solution 
into the ore, but does not assist in bringing it out; in 
fact in very small interstices there is nothing which 
will bring out the solution except heat. Where the 
ore is porous the extraction is greater, and the loss of 
cyanide less than where the ore is tight with very 
small subcapillary openings. In all probability the 
loss of cyanide is in a very great measure due to the 
condition of the ore, rather than to cyanicides; at least 
it would appear so from laboratory tests on small 
quantities of ore where cyanicides can be readily deter¬ 
mined and due allowances made to overcome them. 

During washing there is a dilution of the cyanide 
solutions, a large portion of which cannot be used to 
make up fresh solutions. The consumption in modern 
practice is from ^ to pounds KCN per ton of ore. 

Determination of Cyanide Consumption.—Should the 
consumption of cyanide be high, due to cyanicides, 
the cause may be determined by an analysis of the 
solution. For example, i part by weight of iron con¬ 
sumes 7 parts by weight of potassium cyanide, accord¬ 
ing to the former equation: 

FeS 0 4 + 6 KCN = K 4 Fe(CN) G + K 2 S 0 4 ; 

Fe 6KCN 

56 : 390 — 1 : 7- 


34 


CYANIDE PROCESSES . 


In the case of zinc sulphate: 

ZnS 0 4 + 4KCN = K 2 Zn(CN) 4 + K 2 S 0 4 ; 

Zn4KCN 

65 : 260 =1:4. 

In the case of copper sulphate: 

2 Cu' / S 0 4 + 4KCN = K 8 Cu"(CN) 4 + K 2 S 0 4 ; 

Cu 4KCN 

126 : 260 =1:2. 

There are many reactions which occur in the cyanide 
process not yet understood, for which reason the scope 
of the process is still narrow. Probably the widest field 
for cyanide extraction is yet to be developed, but at 
present its distinctive field lies in the treatment of tailings. 

Salts of aluminium and magnesium act in a different 
manner with potassium cyanide, their hydrates being 
formed with the liberation of hydrocyanic acid, thus: 

A 1 2 (S 0 4 ) 3 + 6KCN + 6 H 2 0 

= A1 2 ( OH ) 6 + 3 K 2 S 0 4 + 6HCN; 
MgS 0 4 + 2 KCN+ 2 H 2 0 = Mg( 0 H) 2 +K 2 S 0 4 + 2 HCN. 

A preliminary alkaline treatment overcomes this 
objectionable feature, their hydrates being precipitated, 
which are then inert towards potassium cyanide, thus: 

MgS0 4 + Ca(OH) 2 = Mg(OH) 2 + CaS 0 4 ; 

insoluble magnesium hydrate and insoluble calcium 
sulphate being formed. ' 

Soluble sulphides, formed by the action of potassium 



CHEMISTRY OF THE OPERATION . 


35 


cyanide on some metallic sulphides, again react to 
some extent on the cyanide, with the formation of 
sulphocyanide of potassium, thus: 

ZnS + 4KCN = K 2 Zn(CN) 4 -f K 2 S; 

K 2 S + KCN + H 2 0 + O = 2KOH + KCNS. 

To determine the cause of the consumption of 
cyanide place 100 grams of the pulp in a wide-mouthed 
bottle, add 200 c.c. of the cyanide solution and agitate 
for fifteen hours. Filter, take 20 c.c. of the filtrate 
(equivalent to 10 grams of ore) and evaporate almost 
to dryness in a porcelain dish. Add some strong sul¬ 
phuric acid, evaporate almost to dryness, and cool. 
Dilute with water, add some hydrochloric acid, and 
heat to effect solution if necessary. The metal in 
solution may now be determined by the usual methods. 

The strong sulphuric acid at a high temperature 
decomposes the metallic cyanides, thus: 

2AgCN -f 3 H 2 S 0 4 -f- 2 H „0 

= Ag 2 S 0 4 + 2 NH 4 HS 0 4 + 2 C 0 2 . 

Strong nitric acid may be used in place of strong 
sulphuric; but hydrochloric cannot be used, as it leaves 
the metal in the form of a double cyanide salt, which 
is soluble. 

The reactions with nitric and hydrochloric acids are: 
AgCN + HN 0 3 + 2 H 2 0 = AgNO s + C 0 2 +NH 3 +H; 

K 4 Fe(CN) 3 + 4IICI = H 4 Fe(CN) 6 + 4KCI. 


30 CYANIDE PROCESSES. 

Determination of the Cause of Non-extraction.—Should 

the above tests show a low percentage of extraction, 
the next step is to determine the cause of this non¬ 
extraction. It may be due to numerous causes, such 
as total destruction of potassium cyanide by certain 
salts of the base metals present in a form readily 
attacked by the potassium cyanide. The gold may be 
in a very coarse state, in which case the solvent action 
of the potassium cyanide will be too slow for the prac¬ 
tical application of the process. The gold may be 
combined or alloyed with tellurium, antimony, bis¬ 
muth, etc., in which case the cyanide is inoperative 
until the combination is broken up. There may be 
piesent soluble sulphides in solution. Gangue, such 
as kaolin or talc, may be present in such quanti¬ 
ties as to effectually prevent percolation. To over¬ 
come these difficulties the following methods may be 
tried: 

In the case of an ore which consumes a large quan¬ 
tity of cyanide, if a preliminary wash with water, weak 
acid, or alkali is ineffective, such ore may be classed 
as one not adapted to the process. 

The coarse-gold difficulty may be overcome by 
amalgamation, either before or after treatment with 
cyanide, which generally results in an excellent ex¬ 
traction. The South African practice may be cited as 
an example. 


CHEMISTRY OF THE OPERATION. 


37 


1 he difficulty due to the presence of bismuth, anti¬ 
mony, etc., in combination or as an alloy with the 
gold, may sometimes be overcome by fine grinding 
and long contact with the cyanide solution; but the 
usual method is to treat the ore to a preliminary roast, 
which converts the gold into a condition in which it is 
readily attacked by cyanide. 

The difficulty due to the presence of soluble sul¬ 
phides can be overcome by the addition of a soluble 
lead salt or the addition of an oxidizing agent. 


CHAPTER IV. 


LABORATORY TESTS. 

Determination of Acidity in Ores.—Should an ore be 
acid, the result will be decomposition of potassium 
cyanide unless this acidity is destroyed before the 
cyanide solution is added. 

SMle Acidity.—Agitate io grams of the pulp for 
io minutes with 50 c.c. of water; filter, and test the 
filtrate with litmus paper for acidity. Should acidity 
be shown, wash the ore until the washings no longer 
give an acid reaction when tested with litmus paper. 
Now titrate the total filtrate with deci-normal caustic 
soda solution, until the neutral point is obtained, using 
litmus as an indicator. 

Latent Acidity .—Transfer the washed ore to a small 
porcelain evaporating-dish; cover with water; add a 
measured excess of deci-normal caustic soda solution ; 
stir and titrate the excess of soda with deci-normal 
acid solution. This gives the latent acidity. 

Total Acidity.— The sum of the above tests gives 
the total acidity, but, as this is frequently all that is 

38 



LABORATORY TESTS. 


39 


required, it may be determined as follows: Introduce 
io grams of the pulp into a stoppered bottle with some 
water, add a measured excess of the caustic soda solu¬ 
tion, agitate for 20 minutes and then titrate back with 
deci-normal acid solution. 

The soluble acidity is due to salts with an acid 
reaction, such as ferrous sulphate, zinc sulphate, 

copper sulphate, etc., or to free sulphuric acid from 

© 

the decomposition of pyrite, to tellurous acid, etc. It 
may be overcome by giving the ore a preliminary wash 
with water. This w'ashing is followed by treatment 
with a weak solution of caustic soda or caustic lime, 
which neutralizes the latent acidity due to basic salts. 
The amount of alkali necessary is determined from the 
quantity of deci-normal soda solution used in the above 
experiments. Unless the ore contains a large amount 
of free acid, the preliminary washing with water may 
be omitted, the total acidity being determined and 
reported in terms of lime. 

Test for the Consumption of Cyanide.—The original 
strength of the stock solution being known, it is only 
necessary to determine its strength after it has been 
used on a lot of ore to arrive at the consumption. 
Introduce 20 grams of ore into a glass-stoppered 
bottle, and, after treating for acidity if necessary, add 
40 c.c. of the regular cyanide leaching solution; next 
agitate for thirty minutes and filter; measure off 20 c.c. 


40 


CYANIDE PROCESSES. 


of the filtrate and determine the amount of undecom¬ 
posed cyanide remaining in the solution. The differ¬ 
ence between the amount of potassium cyanide in 
20 c.c. of the regular leaching solution and the quan¬ 
tity found gives the amount consumed by the 20 grams 
of ore. If the consumption of cyanide is not exces¬ 
sive, or say not over .002 part by weight of the ore, 
the extraction tests can be continued; if more than 

9 

this amount, the ore must be rich, in order to stand 
the expense of the heavy consumption. 

Tests for the Percentage of Extraction.—Two series of 
tests are to be made in this case, one by agitation and 
one by percolation. 

Agitation Test .—Take four wide-mouthed glass- 
stoppered bottles, and place 1 assay ton (29.166 
grams) in each, then add 60 c.c. of the following 
cyanide solutions: 

To No. 1, o. 1 per cent KCN solution. 

< < < i 2,0.3 “ “ i( < ‘ 

“ “ 3, 0.5 “ “ “ “ 

“ “ 4, 0.75 “ “ 

The bottles should not be too large, say 5-ounce 
bottles, and before the solution is added the correction 
for acidity should be made as explained. Allow the 
bottle to stand forty-eight hours, with occasional 
shaking, and then filter off the solution; wash with 


LABORATORY TESTS. 


4i 


water up to original bulk; test an aliquot portion of 
the solution for loss of cyanide; dry the tailings; crush 
them to 100-mesh, and assay. From the assay of the 
original pulp and the assay of the tailings the percen¬ 
tage of extraction can be calculated. 

Another method preferred by some is to assay the 
tailings and also assay the solution; then 

Percentage of Extraction = 

Assay of Solution X 100 
Assay of Solution -f- Assay of Tailings' 

For quick results, the bottles are placed in an 
agitator which is revolved for twenty-four hours. 

Several agitation tests can be carried out in this 
manner, varying the strength of the cyanide solutions 
and using 10-, 20-, 30-, and 40-mesh ores. 

Percolation Tests .—For these tests a glass percolat- 
ing-jar provided with a false bottom covered with a 
double filter-paper will be found convenient. Such an 
apparatus is shown in Fig. 1. Place 1 pound, or 
more, of the pulp (with the proper quantity of the 
neutralizer thoroughly mixed with it) on the filter, and 
add to the charge 230 c.c. of the regular leaching 
solution for each pound of ore taken. Allow the solu¬ 
tion to remain in contact with the ore for twelve hours, 
and then percolate for forty hours, by pouring the 
solution back in the percolating-jar from time to time. 


42 CYANIDE PROCESSES. 

Wash with water until the filtrate reaches the original 
bulk. 

Test the solution for the loss of cyanide; assay a 
portion of the solution and the tailings, and thus deter¬ 



mine the percentage of extraction. The tailings must 
be assayed in the dry way. 

Carry out a series of tests in this manner, varying 
the strength of the cyanide solution, the fineness of the 
ore, and the time of contact from twelve to seventy- 
two hours. 

The results of these experiments will prove whether 
the ore is suitable for the process, and, if so, the 
strength of the solution and size of the screen which 























LABORATORY TESTS. 


43 


will furnish the best extraction in the shortest time 
with the least consumption of cyanide. 

The following formula is given by Furman* for 
convenience in calculating the percentage of extrac¬ 
tion : 


d = 6.43016 — . 

ac 

a — the assay value of the ore in ounces troy per ton 
of 2000 pounds avoirdupois ; 
b — milligrams of gold found in filtrate; 
c = pounds avoirdupois of ore taken for the test; 
d— percentage of extraction. 

To Make up Cyanide Solutions.—The working solu¬ 
tion, called the stock solution, is made up by placing 
solid cyanide of potassium in water. This solution in 
passing through the leaching-vats loses a percentage of 
its strength, which, however, is made up by the addi¬ 
tion of cyanide of potassium. 

Commercial cyanide is seldom pure, and it is there¬ 
fore necessary to use a greater quantity than if it were. 
Suppose the KCN is 85 per cent pure; then J 00 _ 

o 0 

1.176 pounds of the KCN is required to bring the 
standard up to 100 per cent pure. 

One pound of pure KCN dissolved in 100 pounds of 


* Furman’s “ Manual of Assaying.” John Wiley & Sons, 







44 


CYANIDE PROCESSES. 


water makes a i per cent solution; consequently if the 
KCN is but 85 per cent pure it will require 1.176 
pounds to make a 1 per cent solution. 

If a vat contain 100 cubic feet of water, and it be 
desired to make up a solution to 0.5 per cent from 
KCN 85 per cent pure, the quantity required can be 
found as follows: 

100 cu. ft. X 62.5 lbs. = 6250 lbs. water. 

If 100 pounds water require 0.5 pound pure KCN, 
then it will require 1. 176 X 0.5 — .5880 pound of 85 
per cent pure KCN, and by proportion 

100 : 6250 = .588 : 36.75 lbs. KCN. 

Suppose the solution to have passed through the 
leaching and precipitating processes and had run down 
from .5 per cent to .2 per cent, how much additional 
KCN must be added to regenerate the solution ? 

100 : 6250 = 0.3 : 18.75 lbs. pure KCN 

and 

18.75 X 1.176 = 22.05 lbs. 85 per cent KCN 
would be required. 

Stock Cyanide Solutions.—To make up stock solu¬ 
tions the quantity of water in the tank must be 
known, and this is found in tons as follows: 


LABORATORY TESTS. 


45 


Radius of tank in feet squared X 3.1416 X depth in 
feet =: cubic feet; cubic feet of water X 62.5 lbs. ~- 
2000 lbs. = tons of water. Suppose the solution con¬ 
tained .3 per cent KCN; then pounds of water X - 3 -4- 
100 = pounds KCN. Suppose . 15 per cent KCN was 
left after leaching; then pounds of water X .15 -f- 
100 = KCN left, and the difference between the .3 
per cent and . 15 per cent calculations will give the 
fresh KCN to add. 

Strong Solutions may contain from .3 per cent to .7 
per cent KCN. Suppose it is desired to make 20 tons 
of .5 per cent KCN solution from a sump solution 
containing .35 per cent KCN, and the liquor in the 
stock tank used for strengthening contains 20 per cent 
KCN. The quantity of liquor required from the stock 
tank may be found as follows: 

20C5 — .35) 

——---= . 16 tons or 320 pounds. 

Determination of the Free Potassium Cyanide in a 
Solution. —Several methods have been suggested for 
this purpose which give good results. 

A rapid and accurate determination may be made 
by titrating a measured quantity of the solution to be* 
tested with a standard solution of silver nitrate. Silver 
cyanide is formed and immediately redissolves in the 



46 


CYANIDE PROCESSES. 


excess of potassium cyanide. I he reaction is as fol¬ 
lows : 

1. AgN 0 3 + KCN = AgCN + KN 0 3 . 

2. AgCN + KCN = KAg(CN) 2 . 

3 - KAg(CN) 2 + AgN 0 3 = 2AgCN + KNO r 

T he end reaction is reached when a permanent 
white precipitate of silver cyanide is produced. When 
silver nitrate is first added to a solution of potassium 
cyanide a precipitate of silver cyanide is formed which 
dissolves in the presence of any free potassium cyanide. 
The silver nitrate is added until all of the potassium 
cyanide has united with the silver cyanide to form a 
double salt of potassium silver cyanide. If more silver 
nitrate is added than is required to form the double salt, 
a permanent precipitate is formed of silver cyanide, 
which shows sufficient silver nitrate has been added 
for the reaction. 

The end reaction is more distinct when two or three 
drops of a 5 per cent solution of potassium iodide is 
added to the cyanide solution before titration. After 
all the cyanide is converted into the double salt any 
excess of silver nitrate will unite with the potassium 
iodide to form a precipitate of silver iodide. 

Standard Silver Nitrate Solution.—A convenient 
standard solution is one that contains such an amount 
of silver nitrate in each cubic centimeter that when it 


LABORATORY TESTS. 


A 7 


is added to io c.c. of a cyanide solution before a per¬ 
manent precipitate is produced it represents o.i per 
cent of potassium cyanide. 

Preparation of the Standard Silver Nitrate Solution.— 
Take 13.06 grams of silver nitrate and dissolve it in 
1 litre (1000 c.c.) of distilled water. 

Titration.—1. Fill the burette with the standard 
silver nitrate solution. 

2. Fill another burette with the cyanide solution to 
be tested. 

3. Run into a beaker 10 c.c. of the cyanide solution 
and add 25 c.c. of distilled water; add from the silver 
nitrate burette cautiously silver nitrate solution until 
a permanent opalescent precipitate remains after 
thoroughly agitating the solution; two or three drops 
of a solution of potassium iodide added to the beaker 
when the cyanide solution is added will assist in 
determining the end reaction. 

4. Read the number of c.c. of standard silver nitrate 
used and divide by 10; the result is the available 
potassium cyanide in the solution in per cent. 

To illustrate: 

If 10 c.c. of the cyanide solution were used and it 
took 6 c.c. of standard silver nitrate, then tV = 0.6 
per cent KCy. 

If a strong cyanide solution is being tested, 3 or 
4 c.c. can be used for the titration with silver nitrate. 


48 


CYANIDE PROCESSES. 


If 4 c.c. required 6 c.c. of silver nitrate, then 10 c.c. 
of cyanide would require 15 c.c. of standard silver 
nitiate; and 15 divided by 10=: 1.5 percent potassium 
cyanide. 

In testing the strength of the strong solution in the 
dissolving-tank, take 10 c.c. of the strong solution and 
dilute with water to 100 c.c. Take 10 c.c. of this 
solution and titrate with silver nitrate as described 
above. I he number of c.c. of silver nitrate solution 
required will be the per cent of potassium cyanide in 
the strong solution, for the 10 c.c. of the dilute solu¬ 
tion only contained a tenth of the original cyanide 
solution, hence there is no need of dividing by 10. 

Determination of the Free Hydrocyanic Acid in Solu¬ 
tion. To 10 c.c. of the mill solution add 10 c.c. of a 
solution of potassium bicarbonate (containing 15 grams 
of KHCO3 to tlie liter), dilute to 65 or 70 c.c. and 
titrate without the use of potassium iodide as an indi¬ 
cator. Upon the addition of the bicarbonate the fol¬ 
lowing reaction takes place: 

HCN + KHCO s = KCN + C 0 2 + H 2 0 . 

The titration gives the HCN in terms of KCN, and 
KCN x 0.415 = HCN. As this titration gives the 
potassium cyanide and the hydrocyanic acid, the 
difference between this result and that obtained, mul¬ 
tiplied by 0.415, gives the hydrocyanic acid. 


LABORATORY TESTS. 


49 


For each c.c. of mill solution taken i c.c. of the 
potassium bicarbonate solution is used. This will be 
sufficient for solutions containing as much as 0.4 per 
cent of HCN, which is much higher than mill solutions 
usually run, but the excess does no harm. 

I he addition of the bicarbonate solution usually 
causes a distinct turbidity, which should disappear 
when the solution is diluted, giving a clear liquid for 
titration. If, as rarely happens, a faint turbidity 
remains, a duplicate of the solution to be titrated is 
prepared, the end point being shown by the increased 
cloudiness in the titrated solution as compared with the 
blank solution. 

Determination of the Total Simple Cyanides in Solu¬ 
tion.—To 10 c.c. of the mill solution add 10 c.c. of 
half-normal sodium hydrate solution (20 grams of 
NaOH per liter), dilute to 65 or 70 c.c. ; add a few 
drops of the potassium iodide solution, and titrate to 
pale yellow opalescence. The result is the total 
KCN, HCN, and K.,Zn(CN) 4 , in terms of KCN. 
ddie amount of sodium hydrate to be added depends 
principally on the percentage of K 2 Zn(CN) 4 present, 
as a large excess should be avoided. The amount 
given will be sufficient for solutions containing 0.7 
per cent zinc and 0.4 per cent hydrocyanic acid, and 
will answer in all ordinary cases likely to be en¬ 
countered in mill practice. The addition of the 


5o 


CYANIDE PROCESSES. 


sodium hydrate produces a permanent precipitate, but 
the use of potassium iodide as an indicator prevents 
any doubt as to the end reaction. 

Determination of the Ferro-, the Ferri-, and the Sul- 
pho-cyanides in Solution.—The ferrocyanides and the 
sulphocyanides, if desired, may be determined by 
titration with a standard solution of potassium per¬ 
manganate in an acid solution, the reactions being as 
follows: 

ioK 4 FeCN 0 + K 2 Mn 2 0 8 + 8 H,S 0 4 

= ioK 3 FeCN 6 + 6 K,S 0 4 + 2 MnS 0 4 + 9 H 2 0 ; 

10KCNS + 6 K 2 Mn 2 0 8 + i3H 2 SO, 

= i iK 2 S 0 4 -f i 2 MnS 0 4 -j- 10HCN 4- 8 H„ 0 . 

One portion, acidified with sulphuric acid, is titrated, 
the result representing both of the above compound 
cyanides. To a second portion, acidified with sul¬ 
phuric acid, a solution of ferric chloride is added. 
The resulting Prussian blue is filtered off and the filtrate 
titrated with the standard permanganate solution, 
d his second titration gives the potassium sulpho- 
cyanide. 

The permanganate solution should be quite dilute, 
containing not more than from 0.3 to 0.5 grams of 
potassium permanganate to the liter. It may be stand¬ 
ardized by any of the approved methods, and its value 


LABORATORY TESTS. 


5 1 


may be calculated for the compound cyanides accord¬ 
ing to the above equations. 

h erricyanide, if present, may be determined by 
reducing it to ferrocyanide, and then by titration with 
standard potassium permanganate as above. 

Should sulphides be present, the shaking up of the 
solution with moist lead carbonate will produce a black 
precipitate of lead sulphide. When present, they must 
be thus removed, by agitation with lead carbonate and 
filtering off the resulting lead sulphide, before the com¬ 
pound cyanides can be determined. 

Assay of Cyanide Solutions for Gold and Silver.—(i) 
Evaporate 29.2 c.c. of the solution to dryness in a lead 
tray. Roll up the lead and cupel, weighing resulting 
button. Alloy the bead with silver if necessary, and 
part the gold with nitric acid in a porcelain cap¬ 
sule. 

Should the solution contain over 0.2 ounce of gold 
per ton, the lead should be scorified together with a 
little borax glass prior to cupellation. The lead tray 
is made of pure lead-foil. It is about 3 inches long, 

2 inches wide, and b inch deep, and should weigh 
about 20 grams. The tray or boat is placed on an 
asbestos cardboard, that rests on a tripod and has a 
Bunsen burner underneath. 

(2) Evaporate | pint of solution to small bulk; add 
40 grams litharge and evaporate to dryness; transfer 


5 2 


CYANIDE PROCESSES. 


to clay crucible and add 14 grams pulverized glass, 
7 grams soda, and 3 grams argol. Cover with borax, 
fuse, pour, and cool. Cupel lead button; weigh and 
part for gold with HNO s ; weigh. 

(3) Crosse's Method .—Add nitrate of silver to J pint 
KCN until precipitate ceases to form. Decant off' the 
clear solution; filter and dry precipitate. Mix with 
4 grams litharge, 7 grams powdered glass, 7 grams 
soda, and 3 grams argol. Fuse in crucible; pour 
and cupel lead button. Flatten button and part with¬ 
out weighing. Weigh resulting gold. This method 
will not give silver, but is accurate for gold. 

To Test the Strength of Cyanide Solutions by Iodine 
Solutions.—(1) This method depends on the fact that 
when a solution of iodine is added to one of potas¬ 
sium cyanide, the iodine loses its color so long as 
any undecomposed cyanide remains. 

(2) To Make up Standard Iodine Solution. _Use the 

reaction 2I + KCN = KI + ICN. 254 saturates 65, 
and 25.4 = 6.5 in a decinormal solution. 

Therefore, to make a standard solution, weigh out 
2 5-4 grams of iodine, place in a beaker with 200 c.c. 
of water, and add sufficient potassium iodine to com¬ 
pletely dissolve the iodine with frequent shaking. 
When the iodine is dissolved make up to 1000 c.c. 
with pure water, and place in a stoppered bottle. 
Then 1 c.c. = .0065 grm. KCN. 


LABORATORY TESTS. 


53 


(3) The Actual Determination. — (a) Fill a burette 
with standard iodine. 

(b) From another burette measure off 6.5 c.c. of 
cyanide solution to be tested, and to this add carbonic 
acid (20 c.c. of ordinary soda-water will do) to con¬ 
vert the caustic and mono-carbonate alkalies, con¬ 
tained in all commercial cyanide, into bi-carbonates. 

(e) Now run in standard iodine, cautiously and 
slowly, until a slight but permanent yellow color is 
produced. 

(cl) Read off the number of c.c. of standard em¬ 
ployed, divide by 10, and the result will be the per¬ 
centage of KCN required. 

Remarks .—This method does not give reliable re¬ 
sults in the presence of sulphides or when the cyanide 
solution is muddy or discolored. 

To Test the Strength of Cyanide Solutions by Silver 
Nitrate Solutions.—The reaction is as follows: 

AgN 0 3 + KCN = AgCN + KNO a and 
AgCN -f KCN = AgKCN 2 . 

Making up the standard solution from the molecular 
weights, it will be found that 17 grams AgN 0 3 will 
saturate 13 grams KCN; thus 

Molecular weight of AgN 0 3 = \yo — 17. 

Molecular weight of 2KCN = 130 = 13. 

If, therefore, 17 grams AgN 0 3 be dissolved in 1000 


54 


CYANIDE PROCESSES. 


c.c. or i liter of pure water, i c.c. will be equal to 
.013 gram KCN. 

This is a decinormal solution, and to avoid mistakes 
in calculations dissolve 13.07 grams of silver nitrate in 
1000 c.c. of pure water, because 17:13= 13.07 : 10. 

To test a cyanide solution take 10 c.c. and titrate 
with silver nitrate, then divide by 10, and the result 
will be the percentage of potassium cyanide in the 
solution. 

For example, if 10 c.c. required 8 c.c. of silver 
nitrate, 8 -f 10 = 0.8 KCN in the solution being 
tested. 




CHAPTER V. 


THE PLANT FOR CYANIDING. 

The Process. Briefly the cyanide process consists in 
treating suitable raw ores, roasted ores, concentrates, 
slimes, or tailings in vats by solutions of potassic 
cyanide. The ore previous to treatment must be 
crushed, sometimes very fine and sometimes to not 
more than half-inch pieces, depending upon its porosity. 

Tailings or concentrates have been previously 
crushed, and need only be conveyed to the vats for 
treatment. 

Slimes are the result of crushing, and are not sought 
in the process; nevertheless when rich they are to be 
saved and subjected to special treatment. 

If amalgamation is practised, the tailings may be 
conveyed directly to the leaching-vats; but as from 
three to five gallons of water per minute are used in 
stamp-milling, they had better be conveyed to a settler 
and the battery-water drained off. This will also 
remove a portion of the slimes. 

After the ore is placed in vats it is subjected to pre- 

55 


56 


CYANIDE PROCESSES. 


liminary treatment if necessary, and if not, the cyanide 
solution is turned into the vat, when leaching com¬ 
mences at once. After the cyanide has dissolved the 
gold from the ore, the solution is drained from the vat 
and allowed to circulate by gravity, at least in most 
instances, through the MacArthur-Forrest zinc-precipi¬ 
tating boxes, where the gold is precipitated on the zinc 
and from which it is recovered to be refined. The 
solution of cyanide by the time it leaves the zinc-pre¬ 
cipitation boxes has become impoverished, for which 
reason it is drawn off into sump-tanks, and there 
pumped into storage-tanks, where it is strengthened 
as desired by the addition of potassic cyanide. Not 
more than 50 cents’ worth of gold should remain in the 
solution after it leaves the zinc-boxes. 

Location for a Plant.—Wherever possible, the plant 
should be so arranged that advantage may be taken 
of gravity, as this will do away with elevating ma¬ 
chinery and much pumping. However, in some 
instances this is not possible and the plant is built on 
comparatively level ground. Some of the largest 
plants are arranged in the latter way from necessity. 

A simple arrangement is shown in Fig. 2, in which 
^ ai e the leaching-vats; b , the zinc-boxes for precipi¬ 
tating the gold, with the boiler-and pump-house under 
the same roof, r, the sump-tank for the exhausted solu¬ 
tion and which, on account of the smallness of the plant, 



THE FLINT FOR CYANIDING. 


57 


is also the storage and regenerating tank; d is the 
trestle passing over the leaching-tank, and from 
which the ore is charged from tram-cars into the 
tank; e is the tailings-track, for cars into which the 
exhausted tailings are loaded and trammed to the 
dump. The dotted lines represent the pipe-lines from 
the leaching-vat to the zinc-boxes and then to the 
sump-tank. The dotted line from the bottom of the 



sump-tank is the tail-pipe of the pump which draws 
liquor from that tank and pumps it up to the leaching- 
tank. 

The Leaching-vat.—These vats are made of pine or 
spruce, steel or iron California, redwood or Louisiana 
cypress. Vats should be painted with asphalt or 
some other non-metallic and water-proof paint. This 
is not absolutely necessary in the case of wood, but is 
for steel and iron if they are to be preserved. In 
some instances vats have been made of masonry with 
an inside coating of cement. Masonry vats are not, 
however, generally approved, on account of the inability 
to detect leaks and their extra expense over wooden 





























58 


CYANIDE PROCESSES. 


vats. The Pelatan-Clerici vat is made of wood, lined 
inside with cement. It may be possible in case 
cement linings are used to set up chemical action, 
especially with acid ores and faulty cement. Wooden 
tanks lined \\ ith cement would leak in case the cement 
became cracked or injured, because of the impossibility 

of keeping wooden tanks tight when not swelled by 
water. 

On the other hand wooden tanks are sometimes 
condemned because they are constructed poorly, and 
because they are said to absorb the gold in solution. 
The vats are made of enormous size up to 50 feet in 
diameter, and must therefore be placed on strong 

masonry, for such vats will hold many tons of ore and 
water. 

Rectangular tanks are sometimes used, but there is 
difficulty in maintaining tight joints with such tanks; 
nevertheless the largest cyanide plant in the United 
States has rectangular tanks 25x50x5 feet. Owing 
to the difficulty in keeping rectangular wooden tanks 
from leaking, round wooden tanks have been generally 
adopted. These are kept water-tight by numerous 
round iron bands, provided with lugs at each end 
through which a bolt is passed and tightened with a 
nut, as shown in Fig. 3. It will be found cheaper in 
every instance to purchase tanks direct from the 
makers, in knock-down form for transportation, than 


THE PLANT FOR CYAN I DING. 


59 


to build them, and consequently it is not thought 
necessary to go into details of tank construction. The 
writer has had considerable experience with home¬ 
made and manufactured wooden tanks, for which 
reason he recommends the latter to prospective tank- 
users. It stands to reason that one who is engaged 
in the manufacture of tanks as a business is equipped 
for the purpose with machines which make each part 



as nearly true as possible, something the carpenter 
cannot accomplish but can approximate. In regard 
to the manufacture of iron tanks the same applies, 
and hence the details of construction are omitted. 

Filter or False Bottoms.—Filter-frames are shown in 
the bottom of the tank in Fig. 3, the side being cut 
away for that purpose. The old gravel-bed filter has 
been entirely discarded in modern leaching practice for 
such frames, which are built in sections for large vats. 
In such vats the floor slopes gently towards the center 
in order to facilitate drainage, and wooden frames are 
placed as shown at a , Fig. 4. The floor-slats are 


























































6 o 


CYANIDE PROCESSES, 


notched at intervals to permit the solution to circulate 
freely. Upon these slats strong canvas, cocoa-mat¬ 
ting, or burlap is stretched and fastened in, by leaving 
a space for the purpose between the frame and the 
inside periphery of the tank. The canvas having been 



stretched, a rope is driven into the space mentioned, 
which holds the cloth taut and prevents the ore 
running into the bottom of the tank. In large or 
deep tanks there would be too much strain on the 























THE PLANT FOR CYAN I DING. 


61 


canvas, for which reason the perforated boards shown 
at b are placed over the slats a, and upon these the 
canvas c is laid. The flange d is either for a bottom 
discharge-valve worked from the top of the tank, and 
through which the tailings are run off, or for a vacuum 
filter-pump which assists drainage. 

Ore Discharging.—Wherever possible and there is 
plenty of water it is economical to sluice the tailings 
out of the vat through doors in the side or in the 
bottom. In case there is to be 
side discharge, the door shown 
in Fig. 5 is a fairly good pat¬ 
tern. The door-frame is fast¬ 
ened to the tank by bolts and 
nuts, but between it and the 
side of the tank sheet-rubber 



Fig. 5 


gaskets are placed, thus obtaining a water-tight 
joint. The door b is provided with a yoke c, that 
engages when it is closed with the latch d. The latch 
is provided with a thread upon which the large hand- 
wheel nut works to complete the fastening. There 
are other side-discharge gates, but the one illustrated 
is as simple and serviceable as any. Where such 
gates are used there should be at least two to the 
tank. 

In Fig. 6 is shown the butterfly valve, for bottom 
discharge. Where water is scarce or the tailings are 



































































6 2 


CYAN IDF. PROCESSES. 


shovelled out of the tank several such valves will be 
required. 1 he valve shown is known as Butters’ valve. 
When in place it extends up through the vat floor and 
through the filter, so that it in no way interferes with 



percolation. In the cut a is the tank bottom, b a 
plain iron flange which is bolted to a cast-iron nipple 
c, having a flange to correspond with b , and a shoulder 
d on the inner side upon which the hanger e rests. 
This hanger is provided with a screw-thread and a nut 
n for tightening the cover h. The nipple or cylinder 
is about 2 feet in diameter, thus affording ample room 
for the discharge of tailings. 

In some instances the tailings are shovelled over the 






































THE PLANT FOR CYAN I DING. 


6 3 


sides of the vats into tram-cars; in others, for instance 
at the Langlaagte Cyanide Works, near Johannesburg, 
South Africa, the car-bodies are raised from their 
trucks by cranes and lowered into the tanks, loaded 
and raised out to the trucks by the same contrivances. 
In other instances the tailings are kept sufficiently 
wet to permit of their being drawn out through the 
tail-pipe of a centrifugal pump. 

The different arrangements are mentioned here 
because the locations of cyanide plants must necessarily 
vary. Where water is plentiful and there is sufficient 
fall to the tailings-dump, sluicing is to be preferred, 
but even in this case drainage after the dump is 
reached must be considered, for prussic acid in very 
small quantities is not at all healthy for animals or 
individuals. 

At several cyanide works in New Zealand where 
there is a percentage of coarse gold the tailings are 
slowly sluiced over amalgamated plates in order to 
save as much gold as possible. The plates are said 
to be quite expensive, and the recovery seems to war¬ 
rant their continuance. 

Vat-filling.—The methods employed for filling vats 
with ore are as numerous .as the methods of discharg¬ 
ing. In some instances where the ore is dry it is con¬ 
veyed to the tanks by belts or trough conveyors, the 
latter sometimes of the screw type, sometimes of the 


64 


CYANIDE PROCESSES. 


flight type, and again of the bucket type. These 
belt- and scraper-lines can be applied with economy 
and advantage in many cases, so long as the pulp is 
not too wet, although they have not been generally 
adopted, probably from the fact that they do not dis¬ 
tribute the pulp over the vat. The idea of pulp dis¬ 
tribution originally was obtained from chlorination 
practice, where, if it was not loosely and evenly sifted 
into the vat, the gas could not work up through it; 
but in cyanide practice a liquid is being used and there 
is not the necessity for such nicety of distribution, 
especially when the solutions are admitted either from 
above or below but are drained from below. It would 
appeal, then, that vats could be filled with conveyors 
equally as well as from cars, and could assist in the 
distribution in large tanks to a greater extent than 
tram-cars. At some works, to avoid dust,-the ore is 
dampened or soaked oustside the leaching-vat, and at 
others it is washed of acids and neutralized in tanks 
before being charged into leaching-vats; again at other 
plants it is soaked with cyanide solutions before being 
placed in the percolating-vats. This modern practice 
changes the entire complexion of affairs so far as vat- 
charging is concerned, and opens up a field for 
economy by the use of conveyors for the purpose. 

Where tailings from stamp-mills are to be charged 
into vats, they are generally settled and the slimes 


THE PLANT FOR CYANlDING. 65 

washed off. The sands are then washed into the 
leaching-vats and the excess water drained off into 
launders. In such cases the slimes are settled and, if 
valuable, treated separately. This method is practised 
largely in South Africa, where amalgamation precedes 
cyaniding and the ore is stamped wet. 

In what is termed intermediate filling the tailings 
are run direct into tanks, where the sands settle and 
the slimes float away. From these settling-vats the 
tailings are distributed to the leaching-vats. When 
the slope of the ground permits they are run into the 

leaching-vat from a hole in the bottom of the settling- 
tanks. 

Messrs. Rutters and Mein devised a simple reaction- 
wheel, on the principle of the lawn-sprinkler, which is 
effective in evenly distributing the pulp and besides, on 
account of the commotion it causes, keeps the slimes 
floating until they are washed over the sides of a tank 
into a launder. The pulp running out of a series of 
arms causes the wheel to revolve in the opposite direc¬ 
tion from which the pulp discharges. The overflow of 
slimes is continued until the vat is full, and clear water 
is still supplied until they have all been removed. 

Water Required for Leaching.—The arrangement of 
a 75-ton cyanide mill is shown in plan in Fig. 7 and 
in elevation in Fig. 8. By reference to the figures it 
will be seen that there are storage-tanks, gold-solution 


66 


CYANIDE PROCESSES. 


tanks, sump-tanks, settling-tank, and acid-tank. In 
some instances there are stock-tanks where strong 
cyanide solutions are kept to strengthen the standard 
solution as they are pumped from the sump-tank to 
the storage-tanks. 

It will be noticed that the solution-tanks are of less 
size than the leaching-vats, the reason being that the 
latter must contain ore as well as solution. Fine- 
crushed ore will occupy about 28 cubic feet of space to 
the ton, while a ton of water will occupy 32 cubic feet. 
Easy-flowing siliceous pulp will require 80 gallons of 
water per ton of ore; heavy concentrates, about 120 
gallons per ton of ore; the wash-water required is 
about 140 gallons per ton of ore. In lixiviating 80 
gallons per ton of ore should be counted on for solu¬ 
tions, and 140 gallons per ton of ore for wash-water. 

Slimes will retain 240 gallons of water; tailings, 30 
gallons per ton. The loss from evaporation and all 
sources will be about 25 per cent of the water used 
when care is taken to save it for future use. 

Vat Foundations.—The foundations for vats must be 
strong, preferably of masonry, but in case that is not 
feasible strong bents must be used and these must be 
level and, if possible, placed upon masonry, or at least 
concrete. Wooden vats when charged with ore and 
solution are heavy, and if not placed on solid and level 
foundations will rack and leak. This is due in a 


THE PLANT FOR CYAN I DING. 


67 


measure to the chimes in the staves necessary to keep 
the wooden bottoms in place and make tight joints. 
Large lcaching-vats are now made about 5 feet 
deep. 

Precipitating-boxes—The box shown in Fig. 9 is 
the most common in use. It consists of nine compart¬ 
ments about 12 >; 18 inches inside and 20 inches deep, 
made of 2-inch plank outside and ij-inch plank for 
compartments. The box is held together by bolts and 
is coated inside and out with paraffine-paint. The 
boxes are given a slight slope to assist the movement 
of the gold solution which enters the first compartment 
at a, then up and over the partition b, into the second 
compartment at c, and so on up and down to the final 
discharge at d. In the last compartment zinc shavings 
are shown resting on a screen: these shavings are in all 
the compartments through which the solution circu¬ 
lates. The pipes shown in the bottom of each com¬ 
partment are for the purpose of drawing off the 
precipitates and the liquor left in the box when it is 
desired to clean up. Another arrangement for the 
same purpose is to have a launder on the side, covered 
and locked so that the precipitates cannot well be 
stolen. Boxes are sometimes made small and arranged 
in series, but there is little advantage to be derived 
from this, while they are more expensive to install and 
offer more opportunity for leakage. About 50 pounds 


68 


CYANIDE PROCESSES. 


of zinc shavings are required to fill a box of the size 
shown in the figure. 



SECTION THROUGH CENTER 
Fig. 9 

The settling- and acid-tanks are used for treating 
the gold slimes, and will not be more than mentioned 
here. 

Vacuum-filter.—The rate of drainage is very slow, 
ranging with some ores from i to i inch per hour. A 
vat 4 feet deep would require at this rate from 96 to 
48 hours to discharge. For this reason the treatment 
of slimes and clayey ores is impracticable in the 
process now being described. Percolation may be 
hastened by creating a vacuum under the filter by 
means of an air-pump or an injector, and these 
machines are generally used. There is an objection 
to the injector, although it does its work fairly well; 
























































































THE PLANT FOR CYANID1NG. 69 

nevertheless it weakens the solution by the amount of 
steam condensed in working, since all steam passes 
into the solution. 

Pipes.—The solutions are pumped and drained 
through wrought-iron pipes. The pipes for charging 
the vats with solutions vary from 2^ inches for a 
20-feet-diameter vat to 4 inches for a 40-feet-diameter 
vat. 

These pipes have three valves, so that they may 
receive strong or weak solutions, and be drained by a 
third valve when that is necessary. The drainage-pipe 
has a short nipple to which is attached a piece of rubber 
hose in order to drain off weak solutions and keep 
them separate from the strong solutions and vice versa. 
This is done by having double launders passing in 
front of each tank, one compartment of which leads to 
the strong gold-solution tank and the other to the 
weak gold-solution tank. There are usually two lines 
of pipe leading to the leaching-vats from the solution- 
tanks, one for weak and the other for strong solutions. 
There are also weak and strong solution sump-tanks, 
the object being to pass the strong gold solutions 
through a series of tanks, filter-boxes, and sumps back 
to the strong solution storage-tank, and also follow 
the same method with the weak solutions. In case of 
the vacuum-discharge the nipple and hose are not 
used ; the vacuum-pump drains the strong or weak gold 


7o 


CYANIDE PROCESSES. 


solutions from the vats and discharges them into their 
respective tanks. 

A centrifugal pump lifts the solutions from the sump- 
tanks and discharges them into the storage-tanks. A 
special launder is used for conveying the gold slimes 
from the filter-boxes to the acid-tank, where they 
receive special treatment before refining. This launder 
is sometimes made movable, and connects with the 
clean-up launder, previously mentioned, on one side of 
the zinc-box. 

Plan of 75-ton Cyanide Plant.—Fig. 7 shows the 
plan of a 7 5-ton cyanide plant, and Fig. 8 an elevation 
of the same plant. 

There are two storage-tanks, a , 12 feet in diameter 
and 10 or 12 feet deep; four leacliing-vats, b, 25 feet 
in diameter and \\ feet deep; two gold-solution tanks, 

c, 12 feet in diameter and 6 feet deep; two sump-tanks, 

d, 12 feet in diameter and 6 feet deep; five zinc-boxes, 

e , three for the strong solutions and two for the weak 
solutions; each box has nine compartments 24'' X 
18 ' x 15 • The pipes can be traced to their different 
destinations and therefore do not need explanation. 
The launder f has a double compartment; the 
launders g have a single compartment, as do the 
launders h and z. The vacuum-pump is at s , the 
centrifugal pump at w ; the power for running these 
pumps is situated at p. The laboratory is at /, and 








Fig. 8 


[To face page ?0.~] 


















































































































































































































































































































































































































THE PLANT FOR CYANIDING . 


71 


the storeroom at sr. In the clean-up room a is the 
acid-tank; b , the settling-tank; c\ the filter-box; d\ % 
the melting-furnace; and e', the drying-furnace. 

The elevation shows the method of taking all possi¬ 
ble advantage of gravity when leaching. From the 
storage-tank a the solution runs to leaching-tank b , 
to gold-solution tank c , to zinc-boxes e , to sump d , 
by gravity. The gold slimes are also washed from the 
zinc-boxes e, and flow to the acid-tank a' and then to 
the filter-box c by gravity. The engine and vacuum- 
pump with the latter’s pipes are shown at sp , the 
centrifugal pump at w> with its pipe-line n leading to 
the storage-tank. The leaching-vat is discharged at 
the bottom into the sluice t. It will be noticed that 
good retaining-walls, x y step the various terraces, and 
these are of importance to prevent ground running, and 
answer as building foundations at the same time. A 
ditch should be dug at the top of the mill to lead away 
surface-water and prevent its undermining the tanks 
or walls. 

Specifications.—A cheap 20-ton daily plant requires: 

4 leaching-vats, 12 X 4 i feet. 

2 gold-solution tanks, 8x5 f ee t- 

1 sump-tank, 12x5 f eet - 

1 zinc-box, 9 compartments, 24" X 18" X 15A 

Cost of mill for dry crushing and lixiviating 600 
tons per month, $7000. 


72 


CYANIDE PROCESSES. 


Cost of mill for treatment of 600 tons tailings per 
month, $3000. 

A 50-ton-capacity plant, or 1500 tons monthly, 
requires: 

2 storage-tanks, 12x8 feet. 

4 leaching-vats, 20 X 4 $ feet. 

2 gold-solution tanks, 10 X 5 feet. 

2 sump-tanks, 10x5 feet. 

4 zinc-boxes, 2 for strong solutions and 2 for weak 
solutions, each having 9 compartments, 24" X 18" 
X 15". 

Approximate cost of dry-crushing mill, $10,000. 

Mill of same capacity for treating tailings, $5000. 

A 75-ton daily or 2250 tons monthly capacity mill 
requires: 

2 storage-tanks, 12 x 10 feet. 

4 leaching-vats, 25 x 4 i feet. 

2 gold-solution tanks, 12x5 feet. 

2 sump-tanks, 12 x 5 feet. 

5 zinc-boxes, 3 for strong solutions and 2 for weak 
solutions, 9 compartments each, 24" X 1 8" X 15". 

Cost for mill of this capacity when dry-crushing the 
° re , $15,000. When treating tailings, $8000. 

Specifications for 200-ton daily plant or 6000 tons, 
per month: 

2 storage-tanks, 16 x 12 feet. 

6 leaching-vats, 35 x 4 i feet. 


THE PLANT FOR CYAN I DING. 


73 


2 gold-solution tanks, 16 X 5 feet. 

2 sumps, each 16 x 5 feet. 

7 zinc-boxes, 9 compartments each, 24" X 18" X 
15 *3 zinc-boxes for weak and 4 for strong solutions. 

Approximate cost of dry-crushing mill of this 
capacity, $40,000. For tailings, lixiviation only, 
$20,000. 


CHAPTER VI. 


LEACHING THE ORE. 

Agitation—The term ore includes any mineral that 
may be worked at a profit; hence gold ores would 
include slimes and tailings at times. The original 
ideas of MacArthur-Forrest were to agitate the ore in 
the cyanide solution. They suggested no form of 
vessel or mechanical contrivance, but simply stated 
that if the pulp were kept in motion by any convenient 
mechanical stirrer the operation would be hastened. 

Nearly every electrical cyanide process is conducted 
on the lines of agitation. It is conceded that agitation 
lessens the time of extraction and expedites the 
process. It allows the oxygen of the atmosphere to 
act on potassium cyanide in such a way as to unite 
it with gold and form the double salt aurio-potas- 
sic-cyanide, it is also probable that by agitation the 
cyanide can come in contact with the metals more 
readily, thus the so-called rusty gold, or that encased 
in a film of oxide or sulphide, upon receiving the 
slightest scratch that breaks the film will permit the 

74 


LEACHING THE ORE. 


75 


cyanide to attack it, and so dissolve it in quicker 
time. Where ores are coarse and porous, agitation 
would assist the operation, but its great practical use 
will be found with hard and fine ores. When very 
low-grade tailings are treated, or fuel is expensive, 
or where very large vats and ore charges are used, 
mechanical agitation may prove more expensive than 
simple percolation. 

Ores containing tellurides, arsenides, and sulphides 
will give better results if agitated than can be obtained 
by percolation alone. Barrels with arms, similar in 
construction to chlorinating-barrels, also shafts with 
radiating arms, have been used for the purpose of 
agitation. The size of ore-charges treated by agita¬ 
tion is limited to the capacity of the barrels or size of 
the vats and motive power. 

If time be an element of importance, stronger solu¬ 
tions of cyanide may be employed with agitation; but 
as the loss is proportionally greater, it is the customary 
practice to use weaker solutions and economize on 
chemicals. With agitation-barrels it is necessary to 
introduce chemical oxidizing agents, otherwise no time 
will be gained, as has been illustrated by MacLaurin’s 
experiments. 

The pneumatic process is also one of agitation. 

Leaching with Cyanide Solutions.—The percolating 
process is extensively employed for ores, concentrates, 


7(> 


CYANIDE PROCESSES. 


and tailings. The process consists in soaking the ores 
to be treated with cyanide of potassium solutions. 
After soaking or leaching, as it is called, the solution 
is drawn off and another stronger solution is some¬ 
times run on. 

The time required for running off or draining these 
various leaching solutions from the ores depends upon 
the degree of fineness of the ore and its character for 
packing tight, which of course would hinder the 
rapidity of drainage. 

Here it can be seen that uniformity of crushing is 
advantageous, and that the coarser the ore the quicker 
will be the drainage. The liquor is run into the vat 
through the bottom by a pipe connected with a vat 
holding the solutions of various strengths. The solu¬ 
tion rises slowly upwards through the ore until it has 
covered the entire charge of ore in the vat. The 
object of this upward percolation against gravity is 
that by this means the solution permeates the mass 
evenly. The solution is run in slowly to avoid making 
channels in the ore, which would be disadvantageous 
to good downward percolation when drainage takes 
place. The idea is to make the whole quantity of 
liquor rise and fall through the ore evenly, and not up 
or down through channels. 

When tailings, especially tailings containing clay, 
are charged into percolating vats, they are apt to 


LEACHING THE ORE. 


77 


remain lumpy. Cyanide Solutions will not thoroughly 
soak into or penetrate such masses, and as channels 
will be formed the liquor will naturally go the easiest 
way through the ore. A mixture of clean sand with 
the ore will assist percolation in such cases, and this 
proceeding may be necessary with clean concentrates 
and slimes, which would pack, unless broken up in 
this manner, to such an extent that percolation could 
not occur. 

Preliminary Washing.—With ores containing sul¬ 
phates a preliminary washing is necessary, as a partial 
oxidation of iron pyrites produces soluble sulphates 
and free sulphuric acid, both of which are sometimes 
destructive to potassium cyanide. These are washed 
away by water as much as possible, and the remaining 
acids and salts neutralized by caustic soda or quick¬ 
lime. If.the ore does not require more than 3 pounds 
of caustic soda or lime per ton, the preliminary 
washing may be omitted, for this quantity of alkali 
will not effect subsequent precipitation when it enters 
the zinc-boxes with the potassic-cyanide solution 
which follows the neutralizing process. The sulphate 
of lime is less soluble than sulphate of soda and 
hence affects precipitation less; however, it is not 
readily washed away by water, but may form sufficient 
potassium sulphide or sulphate to slightly injure the 
solution or precipitate the gold in solution. 


78 


CYANIDE PROCESSES. 


First Step.— I his may be either the standard leach¬ 
ing - solution or a weak solution, depending upon the 
judgment of the millman. If much potassium cyanide 
is going to be lost, the solution may be a weak one ol 
such a strength that all cyanicicles will be exhausted, 
and the solution as well, since then it may be run to 
waste. Percolation experiments have shown that in 
most cases the solutions will permeate the ore quicker 
when introduced from below rather than from the top 
of the vat. In case the strong solution is the one 
first employed for leaching, the following method is 
advisable: 

Second Step. — After preliminary operations have 
been completed, the ore is soaked with a strong solu¬ 
tion, varying, according to experiments made, from .6 
to .25 per cent KCN. This allows the solution to 
penetrate all parts of the tank and establish a uniform 
density. The solution is now allowed to percolate 
upwards until the pulp is quite thin, when percolation 
downwards is commenced, until the solution being used 
shows, on going out, a loss of two or three points. 
The ore is then allowed to soak in this standard solu¬ 
tion for a length of time which has been determined 
by laboratory experiments to be suited to the ore. 

The strong solution, now the strong-gold solution, 
is drained off into the gold-solution tanks, and at the 
same time a weak solution is run on and percolation 


LEACHING THE ORE. 


79 


continued until the outgoing solution and the weak 
solution in the tank have the same strength. The 
solution is allowed to cover the ore in the vat several 
inches, and after several hours is drawn below the sur¬ 
face of the ore, then allowed to stand this way for one 
hour, when more solution is added to cover the ore in 
the vat. There may be a succession of changes of this 
description, the object being to bring air in contact 
with the ore and thereby hasten the solution of gold. 
The time of percolation with the strong solution is 
usually about twenty-four hours, when it is drained 
and, as stated, a weak solution run on. 

Third Step.—As soon as all the strong-gold solu¬ 
tion has been drained off, the weak solution, varying 
in strength from .1 to .3 per cent, is allowed to re¬ 
main in contact with the ore, after which percolation 
is commenced and continued until a distinct loss of 
cyanide in the solution is noticed. 

Drainage to the weak-gold-solution tank is now com¬ 
menced ; at the same time the third solution is run on. 
When the solution leaving the vat shows the same 
strength as the one entering, drainage is discontinued. 
In some instances a third leaching solution is not con¬ 
sidered necessary, in which case the weak solution is 
displaced with water until it shows, upon testing, not 
more than .03 per cent KCN, and the water wasted or 
used for a preliminary wash. In some cases the ore 


8o 


CYANIDE PROCESSES. 


is not more than barely covered by the solutions, the 
object being in such cases to prevent packing by a 
head of water above the ore; it is, however, advisable 
to cover the ore at least 2 inches with the solutions. 

The strength of the weak solution should not be 
more than one third that of the strong solution. 

Fourth Step.—The third solution is also weak, and 
generally the solution that has passed through the 
process as the second solution in a previous operation. 
It will contain not more than o. i per cent KCN. 
This is allowed to percolate the same as the previous 
solutions and after standing in contact with the ore for 
several hours is drained off. At the same time it is 
draining wash-water is turned on until the solution 
leaving the vat shows no more than .03 per cent KCN. 

This solution can be run through the precipitation- 
boxes, 01 be kept for use and strengthened to answer 
as the second or weak solution in the next leaching, 
the second solution in this case answering as the 
third solution. That there is any advantage in this 
interchange of weak solutions is questionable; how¬ 
ever, it is claimed by some that where gold is in a 
solution the extraction is better, and as very little gold 
is in the third solution, but more than in the second 
which has gone through the zinc-boxes, the practice 
may be advantageous. 

Fifth Step. In case the wash-water is drained off 


LEACHING THE ORE . 


81 


from the ore it can be saved to use as the preliminary 
wash on the next charge. This practice may have the 
advantage of destroying some cyanicides which would 
otherwise attack the strong solution. When used as 
indicated it is run to waste, and in case it is not so 
used it is wasted; otherwise there would be too much 
increase in the bulk of solutions. As little water 
should be used for this purpose as possible, in order to 
prevent an increase in bulk of solutions. 

Sixth Step is the precipitation of the gold from 
solution, but as this is a process by itself it will be 
treated separately. 

The discharge of tailings has been previously men¬ 
tioned under Ore Discharging. 

Time of Leaching,—The rate at which the solution 
percolates through the ore is a question of some im¬ 
portance.- If the ore is such that percolation cannot 
take place at a rate above -J inch per hour, the slimes, 
or whatever it is that packs, must be considered. In 
the case of clayey ores sand must be added to make a 
porous bed. In the case of sulphides a similar mixture 
may be needed, for sulphides may arrange their parti¬ 
cles in such order that liquor can barely pass through 
them. In case slimes are the cause of poor drainage 
they must be washed from the ore, and run off if 
poor, or if rich be saved and treated separately. 

In some cases, such as clayey ores, it may prove 


82 


CYANIDE PROCESSES. 


advantageous to roast them, provided hydraulic cement 
is not formed. 

It is possible that with clayey ores values can only 
be recovered by the agitation processes. 

To prevent packing, the ores are placed in shallow 
leachmg-vats and the solutions are barely allowed to 
cover them. Thq time of leaching must necessarily 
vary with the condition of the ore, and may be 
hastened by increasing the strength of the strong solu¬ 
tion and lessening the number of weak solutions. 

In this practice one at the outset meets the fact that 
with increased strength of solutions there is an 
increased loss in cyanide. This may be shown by the 
following experiments, made upon the same ore and 
exposed to the solutions the same length of time, 
namely, fifteen hours: 


Experiment No. i. 
Per cent KCN solution before. 1.0809 

“ after... 0.5145 

Consumption KCN by difference. 0.5664 

Extraction of gold, milligrams. 0.5 

“ silver, milligrams. 72.45 

Percentage of extraction of total gold 
and silver. y Q 


No. 2 . 
0.5404 
0.0837 
0.4567 

2 -3 

138.4 

86.7 


No. 3. 

o. 1081 
0.0042 
o. 1009 
2.2 

io 3-3 

79.0 


It is evident that the proper strength of the solution 
foi this particular ore would be between that of experi¬ 
ment No. 2 and that of No. 3, since in the latter case 
nearly all the cyanide was consumed and the amount 
was shown to be too small for a maximum extraction. 








LEACHING THE ORE. 83 

It will be noticed that the consumption of cyanide by 
cyanicides did not influence the extraction in this case, 
where in No. 1 experiment it did. 

The rate of percolation with weak solutions is not of 
so vital importance as it is sometimes made to appear, 
for it is essential that the solution should remain in 
contact with the ore until it has dissolved the gold. 
This of course applies only to fine gold, as with coarse 
gold unlimited time would be required, for which 
reason in some instances the tailings are washed slowly 
from the tanks over amalgamated-copper plates; in 
another instance cyanide was fed to the stamp-battery 
in order to commence early on the dissolution of coarse 
gold. 

Roasting Ores to Assist Leaching.—In case the ore is 

to be dry-crushed a dehydrating roast should be given 
it, but not an oxidating roast, for that would produce 
sulphates with all their attendant evils. A dehydrat¬ 
ing roast leaves ores in a porous condition and greatly 
aids cyaniding. 

Such calcining must not exceed 300° F. in tem¬ 
perature; otherwise lime-magnesia ores will produce 
hydraulic cement and prevent percolation. 

The theory of the dehydrating roast is that, the water 
of crystallization being driven off, the subcapillary pores 
in the mineral particles are in a condition to absorb 
the solutions, in fact are opened and do not close. 


8 4 


CYAMIDE PROCESSES. 


In case an oxidizing roast is given the ore, it must 
be thorough, otherwise the oxides will have more or 
less effect upon the solution. Mactear states “that 
the action of KCN on freshly precipitated oxides of 
iron, zinc, copper, and lead is greater than on gold, 
and that carbonates of the above metals are more 
readily soluble than gold.” 

W ith a partial oxidation the sulphates formed com¬ 
plicate the process, consequently the roast must be 
thorough or, as it is termed, “dead,” thereby leaving 
no oxides or sulphates in the ore. 

d he action of alkali solutions upon oxidized ores 
produces hydrated oxides or carbonates which decom¬ 
pose KCN. 

There is no doubt but that many ores will be 
benefited by a dehydrating roast, and still others by a 
dead roast, but this is a matter which can only be 
determined by actual experiment. It is well known 
that the character of an ore changes with depth, and 

that this change may be sufficient to warrant roasting 
before cyaniding. 

Silver Extraction—Roasting.—It is claimed by some 
that roasting hinders the extraction of silver; upon 
what ground this statement is made, and it has refer¬ 
ence to a dehydrating roast, is not recorded, but it 
would appear feasible in case of an oxidizing roast or 


LEACHING THE ORE. 


85 


a chloridizing roast, otherwise the statement needs 
more explanation. 

The treatment of silver by cyaniding does not differ 
much from that of gold; in fact they may be both 
leached with the same solution and at the same time. 
Chloride of silver is much more soluble in KCN solu¬ 
tions than gold, and this fact has led to a patent in 
which it is proposed to chloridize silver ores previous 
to cyaniding. 

Silver seems to be more susceptible to the electrical 
than to the straight cyaniding treatment, and agitation 
also seems to increase its solubility. 

As a rule very rich silver ores are not treated by 
cyaniding, and such silver as is met with in ores is 
mostly sulphide which is difficultly soluble in KCN 
solutions, with the exception of the subsulphide. 
With strong solutions silver is recovered in somewhat 
greater proportions than with weak solutions, yet the 
increased cost of the chemicals will, except in extra¬ 
ordinary cases, prohibit this practice. 


CHAPTER VII. 


PRECIPITATION OF GOLD FROM CYANIDE 

SOLUTIONS. 

Historical.—Having obtained the gold in solution, 
the next step is its recovery in metallic form. 
MacArthur's first patent suggests the evaporation of 
the solution to dryness, and fusing the resulting saline 
residue. Any one acquainted with evaporation on a 
small plan knows how tedious such methods are; but 
when tlie danger from the poisonous fumes are also 

taken into account, it appears at once that this method 
is impracticable. 

MacArthur next considered the feasibility of precipi¬ 
tating the gold with sodium amalgam, but this also 
proved unsatisfactory, as the mercury would oxidize 
quickly and refuse to unite with the gold. 

The crudeness of these methods led to careful 
experiments, which finally settled upon fine filiform 
threads of zinc as the precipitant. This we believe is 
the only patent the MacArtlmr-Forrest people possess 

86 


CYANIDE PRECIPITATION. 87 

which is valid, although much is said of the MacArthur- 
Forrest patents. 

There have been numerous patents to replace zinc 
precipitation, which undoubtedly has faults, but none 
have been universally adopted. 

Mr. Malloy suggested sodium or potassium amal¬ 
gam, formed electrolytically from a solution of car¬ 
bonate in contacc with a bath of mercury. The alkali 
metal was to combine with the cyanogen of the gold, 
forming an alkali salt of cyanogen, while the gold was 
to be instantly amalgamated. The potassium cyanide 
was to be regenerated, but for some reason the patent 
has never been adopted. 

Dr. Johnson used charcoal as a precipitant and 
obtained a patent for the process. The solution was 
run in through a central tube and then came up 
through a filter-bed of charcoal. The gold being pre¬ 
cipitated by the charcoal, the solution flowed away 
clear. By one filter he recovered 25 per cent of gold, 
and by a series of filters 95 per cent of the gold. 
Prof. Christy made some elaborate experiments with 
this process under more favorable conditions than 
would occur in actual practice, and his deductions were 
that Dr. Johnson’s claims could not be verified. He 
says: “ It would seem that a given amount of a certain 
charcoal has a definite capacity of precipitation; that 
within this limit it acts completely and promptly; 


88 


CYANIDE PROCESSES. 


beyond this limit it acts less completely and quickly; 
and that finally it ceases to act at all. “ The pres¬ 
ence of free KCN seems to lower its capacity, and 
perhaps at a certain point stops it altogether; acidifica¬ 
tion seems to increase its capacity.” It was well 
known that charcoal would precipitate gold from solu¬ 
tions, as it had long before been used for precipitating 
gold from chlorine solutions, and the great difficulty 
in the way of its general adoption came from trouble 
experienced in recovering the gold from the charcoal. 
It is not at all probable that this method of precipita¬ 
tion as it now stands will come into general use, 
because of the large quantity of charcoal it requires 
and the difficulty of recovering the gold from the 
charcoal ashes. 

I remy states ‘‘that aurocyanide is precipitated by 
mercuric chloride according to the reaction 

2KAuCN 2 + HgCl 2 = 2AuCN 2 -f 2KCI + Hg.” 

Prof. Christy tried this reaction, and found that 
heating the solution greatly assisted the precipitation. 

1 his method adds so many complications and so 
much expense to the leaching process that it is robbed 
of whatever advantages it may possess; besides in the 

presence of free potassium cyanide precipitation does 
not take place. ” 


CYANIDE PRECIPITATION. 


89 


Precipitation of Gold by Cuprous Salts. (Christy.)— 
“ It must be evident to those who have followed the 
progressive development of the cyanide process that, 
as the method is better understood, the constant 
tendency is towards the use of more and more dilute 
cyanide solutions. While in the beginning a solution 
of 1 per cent was used, this was first reduced to one 
half, then to one quarter, and finally to one tenth and 
even one twentieth of 1 per cent. As the action of 
the so-called ‘ cyanicides ’ contained in the ore is 
better understood and prevented, it seems not unlikely 
that the strength of the solution in potassium cyanide 
may be reduced to one one-hundredth of 1 per cent or 
even lower. It should be remembered that much of 
the material treated by this process does not assay 
over $3 per ton, or only half of one one-thousandth of 
1 per cent gold. So that a ton of solution of 0.01 per 
cent potassium cyanide solution contains thirty times as 
much cyanide as is needed to dissolve $3 worth of gold 
in a ton of ore. 

“The present methods of precipitation, the elec¬ 
trical and the zinc-shavings method, both find in these 
dilute solutions their great difficulty. In the electrical 
process the resistance of such solutions is something 
enormous.* In the case of the zinc shavings it is prac¬ 
tically impossible to precipitate the gold from such a 
solution unless it contains one or two tenths per cent 


* See Electrical Precipitation. 





90 


CYANIDE PROCESSES. 


free cyanide of potassium. This fact alone prevents 
the cyanide from being utilized to the best advantage. 

In order that the cyanide should be utilized to the 
full, we should form the maximum of ICAuCN 2 and 
leave a minimum of free KCN in the solution. This, 
as has been pointed out, is fatal to the precipitation by 
zinc shavings. But it is just here that the cuprous 
method of precipitation comes into play most efficiently. 

In the treatment of such solutions with a bare 
excess of potassium cyanide there is no method of 
precipitation yet invented that can compete with it. 
In such a case there is not enough cyanide of potas¬ 
sium in the solution to bother about saving it. 

The method of procedure would then be as fol¬ 
lows: The solution would be made slightly acid by 
sulphuric or sulphurous acid, as might be most con¬ 
venient. Then there would be added a copper sul¬ 
phate solution with common salt, which had been 
saturated with sulphurous acid. This solution should 
be added until the filtered solution gives a red precipi¬ 
tate with potassium ferrocyanide. The whole solution 
should be thoroughly stirred before this end point is 
determined. A neat way to determine the end point 
is to place a few drops of the stirred mixture on a 
double layer of fine filter-paper. On removing the 
upper layer, a drop of ferrocyanide of potassium will 
give a red precipitate of cuprous ferrocyanide on the 


CYANIDE PRECIPITATION. 


91 


wetted spot of the lower layer when the end point is 
reached. T. his method avoids the delay of filtering the 
solution in the ordinary way. It would, of course, be 
best to determine the end point beforehand with a 
liter of solution, and then add the copper salt to the 
mass of solution, after a preliminary calculation as to 
how much is required. 

“The solution should be allowed to stand for at 
least twelve hours, when it should be filtered. The 
filtrate should stand another twelve hours to see if any 
further precipitate forms; or it may be filtered first 
through CuS, to remove any suspended or dissolved 
gold, and then through old scrap-iron to throw down 
any copper contents. 

“For the recovery of the gold from the cuprous 
aurocyanide, Prof, de Wilde suggests three methods 
as follows: 

“‘First method: Roasting in a reverberatory fur¬ 
nace. One obtains thus a residue of gold and of oxide 
of copper (CuO). This latter is then dissolved in sul¬ 
phuric acid diluted to 20° Baume (or in dilute nitric or 
hydrochloric acid), and the gold remains in the residue 
as pure gold. 

‘ ‘ ‘ At the same time the sulphate of copper is 
regenerated, which will serve to precipitate the gold 
in subsequent operations,* and the same quantity of 


* ‘ “ The sulphate of copper thus regenerated should be crystallized 




92 


CYANIDE PROCESSES . 


copper may continue to serve. Owing to the sharp¬ 
ness of the reactions, the loss of copper will be insig¬ 
nificant. 

‘Second method: Solution of the cuprous cyanide 
in dilute chlorhydric or nitric acid ; there remains a 
residue of aurous cyanide which, after washing and 
drying, is decomposed by heat, and pure gold is left 
behind. 

“‘Third method: The precipitate is heated with 
6o° Baume sulphuric acid in a porcelain or iron pot; it 
is entirely decomposed, leaving a residue of pure 
spongy gold. After cooling water is added, the 
precious metal is washed by decantation, dried, and 
melted. The copper has been transformed into sul¬ 
phate. 

“ ‘ The first method appears to me the most rational, 
the roasting being attempted once or twice a month 
only. It is an inexpensive operation, and the sulphate 
of copper is thus regenerated.’ 

“ In this matter I agree with Prof, de Wilde. After 
being carefully dried the conversion of the cyanide 
takes place very quietly at a low red heat, and the 

by cooling the solution, and the crystals drained from the adherent acid 
mother-liquor. A solution of sulphate of copper containing a notable 
quantity of sulphuric acid is not adapted to the precipitation of gold. 
The mother-liquors, after being strengthened by the addition of sulphuric 
acid, serve very well for the attack of the mixture of oxide of copper and 
gold.’ 






CYANIDE PRECIPITATION. 


93 


spongy, porous, black residue readily dissolves in the 
sulphuric acid, leaving the gold very clean. Care 
should be taken not to alloy the gold and copper by a 
reducing atmosphere and too much heat. 

‘ ‘ A fourth method would be to dissolve both gold 
and copper cyanide in a strong KCN solution, and 
precipitate pure gold by the dynamo. With less than 
2. 5 volts and a strong solution of KCN this is possible, 
the copper remaining in solution. This I have veri¬ 
fied. All the objections to electrolysis apply, except 
that the bulk of the solution would be small and it 
would be concentrated. 

‘ ‘ In many cases it would probably prove more 
advantageous for the reduction-works to ship this pre¬ 
cipitate without attempting to reduce it, as the technical 
skill to do this occasional work is hard to get in mining 
camps. . 

“The methods here outlined will certainly fail in 
the hands of those without chemical knowledge and 
engineering skill, and many unforeseen difficulties will 
probably have to be overcome before they can be 
utilized in practice. Nevertheless I feel very confident 
that in some of the methods here outlined for the pre¬ 
cipitation of gold by means of cuprous salts will be 
found the missing link in the chain of operations 
necessary to utilize the extremely dilute solutions of 
cyanide of potassium, which have been found effective 


94 


CYANIDE PROCESSES. 


in extracting gold from low-grade ores. If this should 

prove to be the case, and the usefulness of the method 

should be extended, particularly in California, my 

native State, I shall feel amply repaid for this long- 
labor. ’ ’ 

Zinc Precipitation—Gold may be precipitated by 
zinc in three ways: first by the use of zinc shavings; 
second by zinc fume, known as blue powder; third by 
zinc amalgam. The action in each case seems to be 
electrolytic, as very small interchange of metals occurs; 
this statement is further substantiated because of the 
hydrogen formed in the precipitation-boxes at the 
cathode of zinc shavings. There is an exchange of 
metals m the electrolyte according to the equation 

2AuKCN 2 -j- Zn = K 2 ZnCN 4 2Au. 

According to the substitution reaction i ounce of 

zinc should precipitate 6.2 ounces of gold, but as a 

practical matter it requires about 12 ounces of zinc to 

precipitate 1 ounce of gold. This has induced chemists 

to look for the discrepancy between theory and prac- 
tice. 

* 

According to the above equation aurio-potassic 
cyanide splits up into KCN, Au, and CN, but there is 
also a tendency to split up into K and AuCN the 
latter acting as an acid radical. If this takes place in 
the presence of zinc and water, the water will be 


CYANIDE PRECIPITATION. 


95 


attacked by the potassium, forming caustic potash 
(KOH) and hydrogen, and the AuCN 2 will be attacked 
by the zinc, forming cyanide of zinc and liberating 
metallic gold. This reaction may occur according to 
the following equation: 

KAuCN 2 + Zn + H 2 0 = ZnCN 2 + KOH + H + Au. 

If this reaction occurs, it accounts for the hydrogen, 
and for the fact that zinc shavings with rough edges 
will precipitate gold, while smooth zinc or thicker zinc 
will not. When the reaction sets in above there is a 
further reaction between the caustic potash and zinc 
cyanide, and potassium zincate is formed. Some 
chemists have stated that at this point a loss occurs 
according to the equation 

K 2 ZnCN 4 + 4 KOH = 4KCN + K 2 Zn 0 2 + 2 H 2 0 , 

but it can be demonstrated by experiment that any 
oxide of zinc and potassium combines with KCN to 
form potassic-zinc-cyanide and caustic potash; for 
example, 

K 2 Zn 0 2 + 4KCN + 2 H 2 0 = K 2 ZnCN 4 + 4KOH, 

which indicates that zinc oxide takes up the cyanide 
although the silver nitrate test would not show it. 
Alfred James considers this a drawback to zinc pre¬ 
cipitation, but sulphides in the ore and in the solu- 


96 


CYANIDE PROCESSES. 


tions will moderate the accumulation of zinc, and if it 
does not, treatment with sodium sulphate and lead salt 
will act as a remedy. 

I he above deductions are made upon the grounds 
that fiee potassium cyanide is in the solution, and this 
is not to be doubted, hence the equation advanced by 
some noted chemists is not possible, viz., 

2ZnCN 2 -f 4KOH = K 2 ZnCN 4 -f K,ZnO, -f 2H..O. 

II of. Christy advances the reaction which takes 
place to be something like this: 

2KAuCN 2 + 3 Zn + 4KCN -f 2 H 2 0 = 

2 Au + 2(ZnCN 2 . 2 KCN) + ZnK 2 0 2 + 4 H. 

However, he does not consider his probable reaction 
demonstrated, and merely advances it to account for 
the extraordinary loss of zinc. There is no absence 
of free potassium cyanide in the zinc-box and hence 
the reaction is void; but if there were no free potassium 
cyanide and caustic potash, 1 ounce of zinc would 
theoretically precipitate 3.1 ounces of gold. 

Influences Governing Zinc Precipitation _ Zinc shav¬ 

ings must be made very thin, in fact they are made 
T2V0 i nc h thick by j nc ] 1 w ^ e j n some cases> an(3 

when of this description 1 pound of zinc will furnish 
1630 square feet of surface, and the consumption will 
be about 5 ounces per ounce of gold. In Fig. 10 is 


CYANIDE PRECIPITATION . 


97 


shown a lathe for turning the zinc shavings. In the 
illustration a is a mandril between the sides of which 
thin discs of as pure zinc as it is possible to obtain are 
placed and clamped tight by the nut b. The lathe has 
three speeds, as shown by the pul ley-wheels e. The 



tool-rest is shown at c, and the guards to prevent the 
shavings flying over the belts at d. Zinc discs can be 
bought ready for turning, at mill-supply depots. 

The solution passing into the zinc-boxes which are 
newly filled has very little effect upon the zinc, but 
when once the action is started it is quite rapid. 

The author has had numerous letters of inquiry from 
students and others stating that they could not precipi¬ 
tate their gold with zinc. His answer was invariably 
that either the zinc was too thick or the solution too 




































































9 8 


CYANIDE PROCESSES. 


weak, and advised that the solution be allowed to 
stand in contact with the zinc some time and then 
strengthened by the addition of potassium cyanide. 
This has always proved efficacious except where the 
zinc has been too thick, precipitation commencing 
almost immediately after the KCN was added. 

The physical condition of zinc has much to do with 
precipitation, for which reason old zinc is better than 
new. The usual practice is to add fresh zinc to the 
last box of the series, and as the zinc in the first box is 
dissolved, move that from the second to the first, and 
from the third to the second, and so on. By this 
means old zinc in an active state meets the solution 
coming from the gold-solution tanks and precipitates 
it quickly. 

Complete precipitation of the gold by zinc has not 
been attained as yet, but as high as 96 per cent is 
obtained. The gold, however, is not lost, and is 
useful in the next solution, for after cyanide solutions 
have taken up a certain amount of gold they seem 
to be quickened and in a condition to dissolve the 
gold in the leaching-vats more rapidly. A. K. Hunt¬ 
ington seems to think that this shows there is real 
utility in using solutions over and over again with¬ 
out extracting all the gold from them. 

Different Strengths of Solutions.—Strong solutions 
act more quickly on zinc than weak, and consequently 


CYANIDE PRECIPITATION. 


99 


there is more cyanide lost, as well as zinc. There can 
be little economy in this practice from the fact that a 
loss of cyanide occurs all along the line from the 
leaching- to the solution-tanks. Leaching should be 
done with the weakest solutions possible, with a high 
extraction, and precipitation should be of secondary 
consideration. In case the solutions are so weak that 
the gold cannot be precipitated (and they must be very 
weak indeed, as .007 per cent solutions have gold pre¬ 
cipitated from them-), free potassium cyanide can be 
added to the solution as it enters the zinc-box and so 
bring up its strength to the precipitation point. 

Impurities in the Gold Solution_The solution as it 

comes to the zinc-boxes contains, besides chemical 
impurities, sediment which is deposited sometimes on 
the zinc and again falls to the bottom of the boxes as 
slime, mixing with the gold and zinc which also fall 
there. It is impossible to remove this sediment 
entirely, even when slimes are washed from the ore, 
but other than in a mechanical way it does not influ¬ 
ence the precipitation or the power of the solution for 
dissolving when strengthened for the next leaching. 
By using the solutions over and over again they 
become very foul and have to be abandoned or settled. 

Rate of Flow.—As noted when the construction of 
zinc-boxes was discussed, the flow into and out of them 
is made continuous. The solution should travel at 
L.ofC. 


IOO 


CYANIDE PROCESSES. 


such a speed that about all the gold will be precipi¬ 
tated, and not faster or slower. There is not much 
danger of the gold being precipitated outside the box 
unless it should occur in the next leaching, which, 
while possible, is not probable. 

Chemical Effects,—In some cases aluminous sub¬ 
stances are thrown down both in the gold-tanks and 
in the precipitation-boxes, and these seem to hinder pre¬ 
cipitation. Caustic alkalies will in a measure hinder pre¬ 
cipitation, particularly soda, for which reason, if it can¬ 
not be thoroughly washed from the ore in preliminary 
treatment, quicklime is preferable as a neutralizer. 

Acidity of the solution has little effect upon precipi¬ 
tation, in fact should prevent the precipitation of some 
base-metal salts if they are present. The presence of 
calcium carbonate and zinc oxide in appreciable quan¬ 
tities would hinder precipitation by coating the zinc, 
and preventing the solution acting properly. Zinc for 
precipitation must not contain arsenic, antimony, or 
much lead, although a small percentage of the latter is 
not injurious. In some cases zinc is placed in a solution 
of acetate of lead of, say, io per cent strength in order 
to cover it with a porous coating of lead. This is termed 
pickling the zinc and is practised to precipitate the 
gold from weak solutions especially in the presence of 
copper, which sometimes prevents gold from precipi¬ 
tating. According to Mr. T. L. Carter, after cutting 


CYANIDE PRECIPITATION. 


TOI 


the zinc in the lathe it is taken to a trough which con¬ 
tains a io per cent solution of acetate of lead, where 
it is submerged and stirred until it becomes of a dark 
hue. 

Dissolved copper deposits more rapidly from weak 

cyanide solutions than strong ones, and soon covers the 

zinc with a bright metallic coating, beginning at the 

% 

lower boxes and gradually working up towards the 
upper ones. 

When the zinc becomes coated with copper the pre¬ 
cipitation is very slow. The remedy in such cases is 
to strengthen the solution by the addition of cyanide, 
but here an excessive use of cyanide occurs, and the 
copper goes into the stock and sump solutions, even¬ 
tually rendering them worthless. 

Lead-coated zinc will effect the perfect precipitation 
of gold and leave the copper even in the weakest solu¬ 
tions, but the resulting bullion becomes impure from 
the lead. 

Objections to the Use of Zinc.—The objections to the 
use of zinc as a precipitant are such as to create con¬ 
siderable comment. It is considered too expensive by 
some, because of the loss of cyanide in the zinc-pre¬ 
cipitating boxes and because it requires so much zinc. 
Others consider it from a different standpoint, namely, 
that the recovery of bullion from its use is too coarse, 
and the recovery by refining too complicated, together 


102 


CYANIDE PROCESSES. 


with a cei tain loss of gold and silver due to refining 
those metals with zinc. The numerous methods sug¬ 
gested do not seem, however, to have driven the zinc- 
precipitating process to the wall, although it may in 
time. 

“Examination of precipitants from a cyanide mill, 
consisting of gold, silver, copper, calcium carbonate, 
and fine shreds of zinc, showed that copper was not in 
a metallic state, because it dissolved with effervescence 
in dilute HC1. ” Mr. Eichbaum observed that zinc 
does not precipitate copper from a solution made with 
potassium cyanide of 98 per cent purity; but on adding 
iron a brisk evolution of gas took place, but no copper 
was precipitated. If an impure cyanide solution is 
used, copper is soon deposited upon the zinc, which is 

no doubt due to caustic or carbonate in the solu¬ 
tion. 

The solution, after gold has been deposited, contains 
zinc, yet the solution, after being used for months, 
does not cause inconvenience. By the addition of 
water the zinc could not saturate the solution, and the 
same is true of alkali carbonate, which, in the absence 
of lime, is continually forming. The white precipitant 
is the result of alkali on zinc, and of the zinc potassic 
oxide on the double cyanide of zinc and potassium, as 
shown by the formula, and which is insoluble. This 
double cyanide of zinc and potassium, being used over 


CYANIDE PRECIPITATION. 103 

again in the percolating-vats, forms, with the iron salts 
in the ore, ferrocyanide of zinc. 

Buckland considers this the reason for constant 
removal of zinc from the solution with the residues. 

This double cyanide of zinc and potassium formed 
during precipitation of gold is not available for dissolv- 
ing gold in new operations, but it does not appear to 
be detrimental to the process when new cyanide solu¬ 
tion is added to it. It does not precipitate gold dis¬ 
solved by a new solution of cyanide. 

Auro-potassic cyanide seems to be a very stable 
compound, and not readily decomposed, as is evident 
since, when once deposited on zinc, the gold does not 
become redissolved so long as zinc is present. 

Francis L. Bosqui, in the Transactions of the Ameri¬ 
can Institute of Mining Engineers, champions the use 
of zinc as follows: 

“ 1. The great consumption of zinc compared with 
the amount of gold precipitated. 

‘ ‘ The record of zinc used at Bodie in the treatment 
of 52,665 tons of tailings indicates a consumption of 
0.22 pound per ton, at a cost of about 3 cents per ton; 
assuming the price of sheet zinc laid down in Bodie to 
be 9.3 cents per pound, and the cost of cutting it about 
4 cents per pound. To be more pertinent, there is a 
consumption of 1.39 pounds of zinc, at a cost of 18.4 
cents, per ounce of gold recovered. Theoretically 


104 


CYANIDE PROCESSES. 


tin's consumption is enormous, for it should require 
only about i pound of zinc to precipitate 6 pounds of 
gold; but economically it is very small, since it means 
a cost of only 3 cents to the ton of tailings. 

“2. The great destruction of potassium cyanide to 
no useful purpose. 

“ It has been often contended that zinc-precipitation 
calls for the use of stronger solutions than might other¬ 
wise be resorted to. Prof. Christy stoutly claims for 
his and for the electrolytic method the one paramount 
advantage that they admit of the use of very dilute 
solutions of potassium cyanide. At Bodie exhaustive 
experimental tests were made by Mr. C. W. Merrill 
to determine the proper strength for a cyanide solution, 
i.e., with respect to its extracting power on Bodie tail¬ 
ings ; and the conclusion was reached that a solution 
containing less than o. 1 per cent cyanide was not so 
available as a stronger one. The fact, then, that solu¬ 
tions containing less than 0.2 per cent cyanide were 
found unavailable for the best extraction in Bodie 
would nullify the chief advantage claimed for both the 
newer methods of precipitation, at least so far as this 
particular camp is concerned. 

“We know that, theoretically, there is a consump¬ 
tion of cyanide during precipitation, that is, during the 
flow of solution through the zinc-boxes. Some writers 
have laid particular stress upon this, as being one great 


CYANIDE PRECIPITATION. 105 

source of cyanide consumption. I have often tried to 
determine just what this consumption is, by making- 
comparative titration tests on a solution flowing into, 
and a solution flowing from, the same zinc-box. I 
have made these tests very frequently and carefully, 
but have never found the slightest difference in quantity 
between the cyanide present in an ingoing solution 
and that present in an outgoing solution, from the 
same zinc-box; the two samples being taken at the 
proper interval of time. I am aware that the reliability 
of the silver-nitrate test, as a delicate method of deter¬ 
mining the amount of cyanide present in a given solu¬ 
tion, has been called into question. But even assuming 
that the presence of zinc in the solution does vitiate 
the test to a certain extent, it is hardly probable that 
the amount of zinc accumulated during a single flow 
through a zinc-box would be sufficient to destroy the 
validity of a comparative test. In fact the quantity of 
zinc present in 80 tons of strong solution, determined 
quantitatively at the end of one of our first season’s 
runs, was so infinitesimal as to preclude any such con¬ 
clusion. 

“ There is still another reason for supposing a com¬ 
parative silver-nitrate test on ingoing and outgoing 
solutions to be reliable, namely, the remarkable coin¬ 
cidence that in each case the well-known precipitate 
came down at precisely the same point in the two test- 


CYANIDE PROCESSES. 


106 

tubes. In other words, the density of the precipitate 
n as exactly the same in the two tubes, when a 
common point was reached on the burette. This 
would hardly occur with such invariable precision if the 
test on outgoing- solution were really vitiated by the 

piesence of zinc accumulated during a single flow 
through a box. 

“ The silver-nitrate test is a very simple and service¬ 
able one, and, so far as I know, has been generally 
retained in practice. Even if it be, in the long run, 
somewhat vitiated by the presence of zinc in the solu¬ 
tions, it still indicates what might be called a ‘ dissolv¬ 
ing strength,’ and is, therefore, for all practical 
purposes, efficient. 

The amount of cyanide present in our strong-solu¬ 
tion sumps averages from 0.14 to 0.16 per cent. As 
there is no perceptible consumption of cyanide in the 
zinc-boxes, it is safe to assume that this deterioration 
of strong solution is due to the action of ‘ cyanicides ’ 
during leaching, and to its dilution by the original 
moisture in the tailings and by the final wash-water. 

“ All solutions containing more than o. 1 per cent of 
KCN are run directly into a ‘strong-gold solution-tank ’; 
those containing less, into a ‘ weak-gold solution-tank. ’ 
The excess of this weaker solution over and above what 
is used in the preliminary leaching is run through a series 
of ‘ waste zinc-boxes ’ and then to waste. This waste 


C YAN IDE P RE Cl PI TA TION. I o 7 

solution averages in strength about 0.05 per cent KCN. 
There are approximately 14 tons of it run to waste in 
twenty-four hours. This may look like an enormous 
consumption of cyanide, but the system, on close 
examination, will be seen to have one great advantage. 
It prevents an excessive and unwieldy accumulation 
of strong solution, while the amount of cyanide in the 
waste is really small, in comparison with what would 
be required to raise it all to standard strength. This 
accumulation of weak solution is unavoidable where 
there is an abundance of water available for wash- 
water, and where practically all the cyanide solution 
in a vat of tailings is displaced before sluicing. 

“ The consumption of cyanide at Bodie on a total 
run of 52,665 tons of tailings was 0.41 pound per ton; 
on the first 41,730 tons it was 0.38 pound per ton. 
The latter figures represent a treatment of 78 tons per 
day for 535 days. From these data we might indicate 
approximately just what the consumption of cyanide is 
in each stage of the process. On a daily treatment of 
78 tons the consumption was 30 pounds. The loss of 
cyanide in spent solution (assuming that 14 tons per 
day go to waste, containing 0.05 per cent of KCN) is 
about 14 pounds. This leaves 16 pounds per day still 
to be accounted for. It was ascertained by tests made 
in percolators on average samples of tailings treated 
that the loss of cyanide in actual leaching is about 0.2 


CYANIDE PROCESSES. 


i o 8 

pound per ton, or 15.6 pounds per day. This leaves 
a balance of 0.4 pound per day or 0.005 pound per 
ton, which we may assume as the loss of cyanide 
during precipitation, a very insignificant amount. 

“ These results are summarized as follows: 


Consumption of KCN in spent solution 

Per day, 
lbs. 

I4.O 

Per ton, 
lbs. 

0.179 

Consumption during actual leaching. . 

15.6 

0.2 

Probable consumption in zinc-boxes. . 

O.4 

0.005 

Total consumption of KCN.. . 

3°.0 

0.384 


“ Of our success in precipitating gold from weak 
solutions I shall speak in its proper place. 

‘'3. The great difficulty of removing zinc and 
cyanogen residues from the gold , thus causing loss in 
melting , and the production of an unclean bullion. 

“ I will admit that this was a great difficulty with 
us at first, and one which, for a time, seemed insur¬ 
mountable. It was necessary to devise some means of 
separating the zinc-sulphate residues from the gold- 
slimes, after the regular treatment with sulphuric acid. 
Various forms of filter were tried. A perforated false 
bottom of wood, packed with sand, was discarded after 
several trials, on account of the impermeability of the 
layer of slimes which formed on top of the sand. A 
filter of asbestos cloth was resorted to, but was likewise 





C YAN IDE P RE ClPI TA TION. I o 9 

discarded. It not only proved to be an imperfect 
filter, but was found completely disintegrated after the 
subsidence of the action of the acid, a result probably 
due to the mechanical untwisting of its fibers during 
the reduction of the zinc. We were obliged at this 
time to use a succession of washes, in order to dilute 
and gradually eliminate the zinc sulphate—allowing 
the slimes to settle completely each time. This 
method, however, was slow and laborious. A Johnson 
filter-press was next introduced. It seemed to act 
fairly well on the slimes before acid treatment, but 
after the destruction of the zinc the gold precipitate 
apparently became too finely divided to admit of filtra¬ 
tion. A film of not more than -§- inch in thickness on 
the canvas discs of the press seemed to offer a very 
complete obstacle to the passage of the clear liquid. 
The pressure against the discs would run up to over 
100 pounds; the press would then have to be opened 
and the discs scraped. This method was found too 
tedious, and was finally abandoned. 

‘‘After many discouraging failures, the following 
modus operandi was adopted, and has since been fol¬ 
lowed with perfect success: 

“The slimes and fine zinc are discharged directly 
from the zinc-boxes into a redwood vat, 6 feet in 
diameter and 2 feet deep. This vat is protected on 
the inside by several coats of paraffine paint, has a 


I IO 


CYANIDE PROCESSES. 


slight bottom incline for drainage, and is provided with 
a 2-inch discharge-valve. Here the slimes are treated 
with sulphuric acid. After the destruction of the zinc, 
the zinc sulphate and the slight excess of acid present 
are diluted by filling the vat with warm water. Within 
an hour the bulk of the precipitate will have settled to 
the bottom. The supernatant liquor, to the amount 
of about 400 gallons, which still contains a small 
amount of gold-slimes in suspension, is then siphoned 
off into a io-ton settling-vat. 

“The gold-slimes are treated with a succession of 
these washes, the supernatant liquor being each time 
drawn off into the settling-vat until the amount of zinc 
sulphate remaining in the slimes is insignificant. The 
liquor siphoned off into the settling-vat, which contains 
only a very small quantity of slimes in proportion to 
the total quantity obtained, is left to settle between 
clean-ups. The clear liquor is drawn off just before a 
succeeding clean-up, and at long intervals the precipi¬ 
tate is gathered from the bottom and melted. 

“The bulk of the slimes is finally discharged from 
the acid-vat into a filter-box. This box is provided, 
about a foot from the top, with a perforated partition’ 

" ''‘eh ^ closely covered with two thicknesses of 
ordinary mill-blanketing. From the compartment 
beneath this filter the air is withdrawn by means of a 
steam-ejector, and the water is thus removed from the 


CYANIDE PRECIPITATION. 


•in 


slimes by suction. At the bottom of the box is a 
i-inch discharge-valve for drawing off the accumulated 
clear liquid. By occasionally scraping the filter- 
blankets the passage of water through them is greatly 
facilitated. These blankets are removed and washed 
after each clean-up, and clean ones are substituted. 
The partially dried slimes from the blankets are then 
completely dried over a furnace and melted in crucibles. 
The zinc residues being thus pretty thoroughly removed 
from the slimes, the difficulties in melting are reduced 
to a minimum. 

‘ ‘ Prof. Christy lays some stress upon the losses in 
melting. There is sure to be some loss from ‘ dust¬ 
ing, ’ especially where there is a high draft in the 
furnace-flues, and where the pots are carelessly charged 
with the dried slimes. 

“ For some time a considerable value went into the 
slag, which had to be shipped to the smelting-works; 
but after a good deal of experimentation a very suit¬ 
able flux has been found, which reduces the slag value 
to almost nothing. A dust-chamber has been con¬ 
structed in connection with the melting-furnace, and 
an effective damper introduced in the course of the flue. 
The latter is closed at each charging of the crucible, 
and ‘ dusting ’ is thus almost entirely avoided. 

“Our loss in melting has never been more than 
barely appreciable; and now, since the introduction of 


11 2 


CYANIDE PROCESSES. 


a dust-chamber and damper, is wholly insignificant. 
1 he wonderfully close correspondence between our 
actual bullion-yield and the extraction indicated by 
careful assays of charged and discharged tailings 
would in itself weaken the supposition of any consider¬ 
able loss in melting. To be sure, our bullion is low- 
grade, but we suffer no inconvenience from this except 
the small increase in cost of transportation and refining 
in proportion to the value of the bars. 

“4. The failure, in certain cases, to precipitate the 
gold. 

“ Prof. Christy probably alludes here, more particu¬ 
larly, to the difficulty in precipitating gold from a 
weak cyanide solution. He says that ‘in the case of 
zinc shavings it is practically impossible to precipitate 
the gold from such a solution unless it contains one or 
two tenths per cent free cyanide of potassium.’ 

“ In Bodie practice it has been found perfectly prac¬ 
ticable to precipitate gold completely from solutions 
containing as little as 0.05 per cent of cyanide. Our 
weak solutions are run through a series of zinc-boxes, 
of ten compartments each, before going to waste. 
Each compartments has a capacity of about 8 pounds 
of zinc shavings. The solution, after passing through 
about 160 pounds of zinc shavings, is found to be 
practically free from gold; repeated assays indicating 
merely a trace. 


« 


CYANIDE PRECIPITATION. 113 

\ 

“ At the Victor plant, of 50 tons per day capacity, 
considerable difficulty was experienced in precipitating 
gold from weak solutions; but by the addition of a 
third box, making an aggregate of thirty compart¬ 
ments, the trouble was corrected and most satisfactory 
precipitation was obtained. 

‘ ‘ The following table of assays made at random on 
solution samples from various zinc-boxes at different 
intervals in the season’s run indicates a high percentage 
of precipitation in both strong- and weak-solution 
boxes. These results were obtained by evaporating 
250 c.c. (about 8 assay tons) of the solution in each 
case, and assaying the residues. 



Strong or Weak. 

Value of the 
Ingoing Solution 
per Ton. 

Value of the 
Outgoing Solution 
per Ton. 



Au. 

Ag. 

Total 

Au. 

Ag. 

Total 

I 

Strong (0.14 to 0.16 per cent.) . 

$4.24 

$•45 

$4.69 

$•05 

$ .02 

$.07 

2 

• • • • » • * 

4-39 

•43 

4.82 

. IO 

.03 

•13 

3 

4 

5 

ftt 41 44 44 

44 44 44 44 

4-03 

4.13 

3-32 

•44 

.46 

.38 

4-47 

4-59 

3.70 

Trace 
Trace 
. 10 

.06 

.16 

6 


3 05 

•39 

3-44 

.26 

.07 

•33 

7 

8 

Weak (0.04 to 0.07 per cent.). 

44 44 4* 44 

1.24 

2.90 

.14 

•45 

1.38 

3-35 

Trace 

.07 

.07 

•M 

*9 


3.82 

•57 

4-39 

• 25 

.07 

•32 

*10 


4 • T 3 

.64 

4-77 

.21 

.08 

.29 

*1 I 
*12 

44 44 44 44 

44 44 44 44 

I .14 

•52 

. l6 

•15 

I .^O 

.67 

Trace 
T race 

. 


* We have occasionally been puzzled by the appearance in our zinc-boxes of a 
yellow, aluminous (?) precipitate, which seems to be thrown down in the gold- 
tanks as soon as the solution leaves the vats. Whenever this accumulates to any 
extent it interferes somewhat with precipitation. Assays Nos. 9 and 10 were made 
on solutions taken from a box containing a considerable amount of this aluminous 
slime. The slightly lower percentage of precipitation is apparent. The two 
following assays (Nos. 11 and 12) were made on a low-grade solution flowing 
through the same box, after a complete elimination of the aluminous material, 
and indicate a normal precipitation. 










































CYANIDE PROCESSES. 


114 

Precipitation with Zinc Fume.— This process is 
adopted at Delamar, Idaho, and Mercur, Utah. The 
action of zinc fume is almost instantaneous, but when 
used for precipitating, the cyanide solution is agitated 
by compressed air, for the purpose of stirring up any 
residues remaining in the bottom of the precipitation- 
tank from former operations. The zinc fume, which 
■s the volatile zinc from smelting operations that has 
een condensed and caught in the flues, contains about 
90 per cent zinc. For the purpose of gold precipita¬ 
tion ,t ,s sifted into the tanks at intervals during 
agitation. Five pounds of zinc fume, or blue powder 
as it ,s called, will precipitate the gold from 30 tons 
of cyanide solution at Mercur; the quantity of gold in 
the solution, however, is not stated. From other 
sources it is claimed that from 6 to 19 ounces of zinc 
fume will precipitate i ounce of gold. 

. A CaSe ° f COnsiderab le interest regarding the use of 
zinc dust or fume as a precipitant of gold and silver 
rom cyanide solutions was recently decided bv the 
United States District Court for Idaho. The court 
deeded against the plaintiff and held that the patent 
was anticipated by prior publications and patents 

hOSC 7 hing t0 USe the P roc ess may be interested to 
know what are the claims of the patent in question, as 

well as something of what was known regarding this 

use of zinc dust prior to the application for the patent 


CYANIDE PRECIPITATION. 


IT 5 


UNITED STATES PATENT NO. 607,719 FILED 

MARCH 9, 1896. 

“Claim 1. The process of extracting precious 
metals from cyanide solutions, which consists in treat¬ 
ing said solutions with zinc dust, to wit, the herein- 
described material composed of zinc and zinc oxide, in 
a state of agitation, substantially as described. 

“Claim 2. In the process of extracting precious 
metals from cyanide solutions the use as a precipitat¬ 
ing reagent of a definite quantity of zinc dust in a state 
of agitation, the quantity of said zinc dust being sup¬ 
plied in only a sufficient quantity to thoroughly precipi¬ 
tate the contained metals, substantially as described. 

“ Claim 3. The process of extracting and recovering 
precious metals from their ores and which consists 
essentially of the following steps: First, subjecting the 
ore in a powdered state to the action of an aqueous 
solution of a cyanide; second, supplying to the solu¬ 
tion charged with the precious metals that quantity of 
zinc dust determined to be exactly sufficient to precipi¬ 
tate said metals; third, agitating said solution and said 
zinc dust until said metals are precipitated and said 
zinc dust is absorbed; fourth, recovering the precious 
metals from the valuable precipitate of the preceding 
steps by filtration or other process, substantially as 
described. 


CYANIDE PROCESSES. 


116 


In a paper read by Mr. H. L. Sulman before the 
Institution of Mining and Metallurgy (London) on 
February 20, 1895, he says that all the conditions are 
fulfilled “ by the product known as zinc fume. ... It 
L a commercial by-product, . . . being condensed 
metallic zinc vapor in a state of extreme division.’’ 

It is an impalpable powder more or less coated with 
oxide, which somewhat retards the precipitating action 
unless treated with dilute ammonia or some similar 
solvent to clean the zinc.” “ A small portion of this 
preparation agitated with a very dilute solution of 
auro-potassic cyanide permeates the whole volume of 
liquor, rendering it slightly and uniformly cloudy . 
and almost immediately determines the precipitation of 
the gold. ” “I have treated gold solutions of varying 
strengths of cyanide and with an expenditure of zinc 
fume never exceeding o. 5 pound per ton of ore, and 
have obtained precipitates which seldom contained 
below 97 to 98 per cent of the gold originally present 
in the liquor.” “When the solutions are rich in 
metal (or over 0.3 ounce per ton) the addition of zinc 
fume of from three to four times the weight of gold 
present has been sufficient to completely precipitate 
the latter. Very dilute solutions, strangely enough, 
require rather more than this.” 

It will be seen from the quotations given that every 
claim of the Waldstein patent is anticipated by Sul- 


CYANIDE PRECIPITATION. 117 

man. The only difference between the two is in 
Sulman’s treatment of the zinc dust with an ammoniacal 
solution to remove the oxide. His United States 
Patent No. 576,173, filed February 25, 1895, also 
clearly shows that he did not consider it possible to 
patent the use of zinc dust alone as a precipitant, for 
all he attempts to cover in his patent is the process for 
removing - the zinc oxide so as to make the zinc more 
active, and a special form of apparatus in which to 
make the precipitation. The price of zinc dust is from 
6 to 7 cents per pound. 


CHAPTER VIII. 


TREATMENT OF BULLION. 

Melting Gold Precipitates—Having deposited the 
gold upon zinc, the next process is to recover it in the 
form of bullion. The gold is deposited as a black 
slimy mass, and the zinc with the gold adhering is 
shaken in water, when the gold and some of the zinc 
fall off. The water is next drained off through a filter, 
and the fibrous particles of zinc collected in a sieve 
and shaken again to remove gold. The last sifting 
removes the coarse zinc from the precipitates, which 
now contain gold, silver, and zinc, and, if the residues 
m the filter-boxes are added, other metals and impuri¬ 
ties. This precipitate is thoroughly dried and roasted 
slowly, care being taken that the flame does not come 
in contact with the mass. After being thoroughly 
dried it may be refined by the “calcining and roasting 
process ” or recovered by the “acid process.” 

The roasting process is used where oxidation of base 
metals has not been complete. At Johannisburg, 
South Africa, the acid treatment is not employed, as it 

118 


TREATMENT OF BULLION. 119 

involves washing and filtration of the slimes, with loss 
of gold by formation of regulus in melting, if sulphates 
remain in the slimes by fault of imperfect washing. 
The practice is to dry the slimes to dust nearly 5 
then to thoroughly mix them with powdred niter, the 
amount varying from 3 to 33 per cent of their weight, 
and this mass is gently heated on a wrought-iron tray. 
The flames must not come in contact with the slimes, 
and the gases should be conducted up a flue away from 
the operator. By the use of niter everything connected 
with the precipitate is refined. After this oxidation 
the roasted mass is placed in plumbago crucibles with 
the proper fluxes. 

When metallic oxides are present, the flux is com¬ 
posed of six parts roasted niter slimes, four parts 
borax, two parts soda, one part sand. When only a 
small amount of metallic oxide is present the charge 
may be three parts slimes, one part borax, two parts 
soda, one part sand. The function of the sand is to 
form a fusible slag with soda, and protect the pots from 
metallic oxides and potash formed by the reduction of 
the niter. The slag resulting from the melting of these 
slimes usually contains more or less gold; it is there¬ 
fore crushed and sent to the smelters. At some mills 
these slags are crushed and panned for gold, and the 
tailings sent to the smelter. Fluxes which give clean 
fluid slag are preferable in this as in any other refining. 


I 20 


CYANIDE PROCESSES. 


The crucible previously annealed is placed on a flat 
fire-clay tile resting on the bars of the refining-furnace. 
A charge of precipitates is then put in the crucible, 
and as they subside fresh precipitates are added. 
When the crucible is two thirds full, the slag is 
skimmed off and fresh portions of precipitates added 
until it is three fourths full of molten bullion. 

The crucible is then removed from the furnace, and 
the contents poured into ingot-molds which have been 
previously heated and oiled. All excess of oil should 
be wiped out of the mold before pouring the metal. 
It is sometimes advisable to smelt the bullion a second 
time if much zinc is present with the gold, and as zinc 
and gold form a very poor alloy it should be carried 
on at a low heat. 

Sulphuric Acid Treatment—This method of treating 

gold precipitates is practiced chiefly in the United 
States, but is being adopted in South Africa and New 
Zealand. For the sulphuric acid treatment wooden 
tubs are sufficient; after the precipitates have been 
thoroughly washed with water they are run into the 
acid-tank shown in Fig. 7, A. The precipitate is very 
slimy, in fact the freer it is from zinc the more slimy 
it is. The quantity of dilute sulphuric acid used to 
dissolve the zinc will depend upon the quantity of zinc 
in the slimes. The acid should not be too stron (T * 
possibly one part acid and ten parts water will be 


TREATMENT OF BULLION. 


12 1 


sufficient, as it has been found that this strength will 
create an action sufficient to produce heat enough to 
make the operation speedy and satisfactory without the 
aid of outside heat. After the zinc has dissolved no 
more hydrogen gas will be evolved, but before decant¬ 
ing the mixture should be stirred, to make sure that 
all zinc has been dissolved. The last traces of metal 
zinc having been removed, the solid precipitates are 
allowed to settle, the liquor then being decanted off, 
and the residues washed into the filter, where they 
are thoroughly rinsed. The bullion is then partially 
dried on the vacuum-filter. 

Should any zinc remain, its presence in melting the 
bullion will cause a mechanical loss of gold, as the 
zinc will volatilize in the crucible-furnace. 

For this reason some treat the slimes first with a 
weak acid solution and then with a stronger acid solu¬ 
tion. 

The mass, after partially drying in the filter, is dried 
at a low heat in a small muffleTurnace, and when the 
moisture is driven off the heat is increased to a dark 
red. 

Oxidation of the base metals which have escaped 
removal by acid treatment should be complete after 
one hour’s roasting, the mass presenting a gray-brown 
appearance. The roasted bullion is transferred to a 
wrought-iron box to be cooled, after which it is 


122 


C YAM IDE PROCESSES. 


pulverized. Borax glass and soda are added to make 
a clear slag. The roasted precipitates are then charged 
into a plumbago crucible previously primed with borax. 
As the mixture sinks in the crucible more roasted pre¬ 
cipitates are added from time to time, d he melting 
usually takes place rapidly. The temperature is kept 
high for some time, to give the small bullion globules 
time to collect. The contents of the crucible are then 
poured into a heated mould and allowed to cool. It 
is claimed that this acid treatment has advantages 
over the calcining treatment, being simpler and allow¬ 
ing the plumbago crucibles to be repeatedly used; 
also the bullion is finer and by care recovered without 
chemical loss. 

Removing Zinc Sulphate.—After the zinc in the gold- 
slimes has been converted into sulphate of zinc by the 
sulphuric acid treatment, the solution is allowed to 
stand a few hours, and is then diluted with hot water 
and stirred. The sulphate of zinc, which is soluble in 
hot water, is gotten in solution and is siphoned off into 
the settling-tank as soon as the undissolved precipitates 
have settled. The precipitates in the acid-tank are 
thoroughly washed several times to remove traces of 
zinc sulphate, after which they are drawn into the 
filter-tank, and washed and dried by suction. The 
precipitates from the settling-tank are also drawn into 
the filter-box and washed there with hot water. 


TREATMENT OF BULLION. 


123 


In some works the solutions used are passed directly 
to filter-presses, and the slimes obtained at once. 

Filter-tank. Where large quantities of precipitates 
are to be dealt with, the slime settling and decanting 
are too slow, for which reason the vacuum-filter or the 
filter-press is adopted, and the separation of slimes 
from the acid and the wash-water hastened. A vacuum 
slime-filter is shown in Fig. 11. It consists of an iron 
tank divided into two compartments, a and /?, by a 
filter bottom, c } of wood which rests upon a central 




Fig. 11 


post, d , and a ledge in the tank. Upon the wooden 
filter bottom heavy duck is placed, and upon it the 
slimes to be washed and treated. 

As shown in Fig. 8, the filter is connected at e with 
an exhaust-pipe leading to the vacuum-pump, and is 
also provided with a discharge-pipe connection, //, and 
a water-gauge, g. The object of the gauge is to indi- 
























































































































124 


CYANIDE PROCESSES . 


cate the height of the water in the lower chamber, /?, as 
the water must be discharged before it reaches the 
height of the exhaust-pipe e. 

Bullion Produced.—1 he bullion produced by the 
cyanide process must necessarily vary according to the 
grade of ore treated, and care taken for its recovery 
and refining. While one will recover bullion 950 fine, 
another can obtain only 750 fine or less. This case is 
important, since it may be more expensive in the end, 
as purchasers of bullion pay for its assay value, and 
refiners’ charges are more for base bullion than fine; 
under such conditions it may be profitable to use care. 
Bullion precipitated by zinc has objections which 
can be overcome to some extent by close application 
to details, although at times they are in a measure 
unavoidable. The loss of bullion from smelting is one 
of the most objectionable features; the loss of zinc 
does not amount to much; the loss of cyanide is a 
bad feature, but unavoidable. 


CHAPTER IX. 


TREATMENT OF CONCENTRATES AND SLIMES. 

Auriferous Sulphurets.—Under this heading are to 
be classed clean pyrites produced by concentration. 
When such pyrites are free from acid salts they can be 
treated satisfactorily in some cases, in others not, 
especially when copper is present. It is always advis¬ 
able to keep concentrates of this description away from 
the air, for they will oxidize quickly, for which reason 
in South Africa they are kept under water. In the 
treatment of such ores it may be well to percolate with 
a weak solution hi st, and by this means obtain a larger 
extraction' with less loss of cyanide from the strong- 
solution following. The poor results sometimes 
obtained in the treatment of concentrates may be from 
not allowing sufficient time for the solutions to act 
upon them or not crushing fine enough. 

In crushing sulphurets fine there is great danger of 
their sliming, they are much more brittle, and more 
easily pulverized than the remainder of the ore. When 
very fine they are also more difficult to size and con¬ 
centrate. 


125 


126 


CYANIDE PROCESSES. 


It is possible to treat these concentrates by cyanide, 
but, being - generally richer in metal, their treatment 
requires longer time for the best results. As their 
quantity is limited, the size of the plant need not be 
as extensive as where the whole mass of tailings is to 
be tieated. Agitation will hasten the cyaniding of 
concentrates. Percolation with concentrates requires 
twenty days, because of the difficulty the solution 
encounteis in passing through the coarse particles of 
ore. “Difficulty sometimes arises owing to the 
crystalline form of iron pyrites and galena. These 
mineials crystallize in cubes, and in fluids arrange 

o 

themselves face to face, so that a section of such a 
mass deposited from fluid would resemble a brick 
vail in structure. Dr. A. Scheidel suggested mix¬ 
ing coarse sand with the cubes to overcome the 
difficulty. 

I he results of the experiments made upon tailings 
containing sulphurets by the California State Bureau 
of Mining are here given. A i per cent solution of 
potassium cyanide was used for the experiments. 

The experiments illustrate the effect of time and 
strength of the solution, while they also illustrate that 
the solution is not impaired in its action when sulphides 
only are present, both of which are important items in 
considering the scope of the process. 


TREATMENT OF CONCENTRATES AND SLIMES. 127 


Treatment lasting 2 hrs.: tailings retained 35.29$ gold. 


31 - 37 * “ 

30.37$ “ 

25.49$ “ 

21.56$ “ 

Another portion from the same lot of sulphurets 
ground and passed through a 100-mesh screen (the 
former having been passed through a 60-mesh screen) 
were then treated six hours. There was left in the 
tailings after this latter treatment 17.64 per cent of 
gold, showing that fineness of the ore in this case 
materially aided digestion. 

To ascertain whether dilute cyanide would extract 
all the gold in these sulphurets the ore was ground in 
an agate mortar to impalpable powder, and digested 
for forty-eight hours with three different solutions of 
1 per cent cyanide, after which treatment the tailings 
were found to contain 9.8 per cent of gold. 

Another lot of sulphurets from which free gold had 
been removed with great care was subjected to a 
1 per cent solution after passing a 120-mesh screen. 
Treatment lasting 2 hrs. : tailings retained 31.2$ gold. 


6 “ 
8 “ 


i i 


3 

4 “ 

5 “ 

8 “ 


* * 


* 4 


< < 


4 4 


4 4 

4 4 

4 4 

4 4 


28.5$ 
i 5 - 
* 5 - 


4 4 


4 4 


4 4 


4 4 


10.4$ 


128 


CYANIDE PROCESSES. 


The deductions to be made by comparison with the 
6o-mesh screen experiments are that double the fine¬ 
ness lessens the time by one half in the treatment of 
ore by cyanide solutions of the same strength. 

Treatment of Slimes.—During the process of wet 
stamping a large portion of the ore is converted into 
impalpable powder, which is difficult to settle and 
difficult to treat with the sands. In one instance when 
stamping to a 30-mesh sceen 74.28 per cent of the 
total was so fine that it passed through an 80-mesh 
screen having 6400 holes to the square inch, and 
carrying with it about 75 per cent of the gold. 

In another case when crushing dry with rolls from 
2 to 1 inch, 47-8 per cent went through a 20-mesh 
screen, and when crushing below J inch 77 per cent 
went through a 20-mesh screen. The latter was 
pyritic 01 e, which in a measure accounts for the 
increased quantities of fine particles. This is not 
unusual, and if dry crushing be practiced in a stamp- 

mill, a further percentage of the ore will be reduced 
to slimes. 

Millmen understanding these features crush their ore 
as coarse as is consistent with good extraction by 
leaching. 

As stated, the conditions that govern coarse crush¬ 
ing are porosity and roasting, so that from ores of the 
above description the best results are obtained. Ores 


TREATMENT OF CONCENTRATES AND SLIMES. 129 

which are crushed fine or coarse as to that matter are 
but imperfectly leached unless sized, the solutions in 
such cases circulating in channels or between the 
larger particles rather than through the fine ore. 
If during the process of drainage much fine ore is 
present, it will prevent the operation, even when a 
vacuum filter-pump is attached to the vat. 

In the latter case there are three methods of dealing 
with the problem, namely, separation of the slimes 
from the ore and treating each separately; agitation, 
by which means slimes and ore are treated together * 
and finally filter-press treatment, in which slimes only 
are treated. 

Decantation Treatment of Slimes.—In this method of 
treatment the slimes are washed from the ore delivered 
to the tanks by the automatic ore-distributor mentioned 
in Chapter' V. The water carrying the slimes is con¬ 
ducted to the settling-boxes, which are usually large 
pointed boxes arranged in series, the first box say 
20 r X 20' by 10' deep, the second 30" X 30' X 10' 
deep, and the third 40' X 40' X 10' deep. The 
heaviest slimes settle in the first box, the next heaviest 
in the second, and the lightest in the last. Slime 
settling may be hastened in some cases by the addition 
of lime-water, in others by alum. 

The settled slimes are drawn off from the bottom 
and pumped into the first two of eight treatment-tanks, 


T 3 ° 


CYANIDE PROCESSES. 


about 90 per cent of the water from which they were 
settled having been separated. 

The treatment-vats have a conical bottom, and more 
water having been separated from the slimes by allow¬ 
ing them to settle, they are sluiced into a pump by a 
jet of cyanide solution and transferred to a second series 
of vats containing 0.01 KCN solution. 

About 80 per cent of the gold is dissolved in the 
passage through the pumps, but agitation is continued 
for about two hours by withdrawing the solution at the 
bottom and discharging it in oblique jets at the top and 
through the sides. The slimes are then allowed to 
settle, and the clear solution drawn off through side 
valves in the tank or by a siphon, and passed to the 
precipitation-boxes. 

The residual slimes are then pumped in succession 
to the third and fourth series of two vats, where they 
are fur ther agitated with very dilute solutions of cyanide 
and allowed to settle. These solutions do not pass to 
the precipitation-boxes, but are transferred to the pre¬ 
ceding series of vats. 

A somewhat similar method is practised in South 
Africa. The cost of pumping the solution for the pur¬ 
pose of agitation is about 10 cents per ton, with the 
total labor cost less than 25 cents. 

T he settlement of the slimes and the decantation of 
the water, which may be returned at once to the mill, 


TREATMENT OF CONCENTRATES AND SLIMES. 131 

will lessen the consumption of water one half, if that is 
any object. 

Slimes and Water. —Slimes will retain considerable 
more water than ore, and without recourse to a filter- 
press cannot be relieved of it. The capacity of tanks 
for slimes containing certain percentages of water are 
as follows: 


1 part slimes to 1 part water 50 cu. ft. space per ton. 


1 

1 “ 

1 


4 4 

4 4 


4 4 

4 4 


4 

5 


4 4 

4 4 


“ 10 “ 


“ 139 “ 

“ I// “ 

9 

“ 354 “ 


«< * < «< 

a < 4 i < 

« i a (( 


4 4 


44 


4 < 


20 


4 i 


4 4 


710 


4 4 


4 4 


4 4 


4 4 


Filter-press Slime Treatment. —The slimes are sep¬ 
arated from ore by means of the automatic charging 
device and are settled in V-shaped boxes. The 
settled slimes are drawn off and agitated in mixing- 
vats for a time sufficiently long to dissolve the gold. 
The slimes are then run into a tank and forced by 
compressed air through the filter-presses. By this 
means 70 per cent of the solution is clear enough for 
immediate precipitation. 

The slimes may also be washed in the press and the 
water immediately used if necessary for the next agita¬ 
tion. 

It is claimed that dissolution of the gold will take 
place in the presses, but the proper treatment seems 


T 3 “ 


CYANIDE PROCESSES. 


to be to dissolve the gold by solution before it enters 
the presses. 

Agitation Processes.—These processes are suited to 
clayey ores, and to them belong the Pelatan-Clerici, 
Gilmour-\ oung, and the Pneumatic processes. 

The Pelatan-Clerici process is electrochemical and 
will be described in another chapter. 

The Gilmour-Young process consists in grinding ore 
previously crushed to pass 30-mesh screen, in Boss 
amalgamating-pans. 

The dry-crushed ore is charged into a pan in 2-ton 
lots, with 100 gallons of water, to form a very thick 
pulp. From two to six bottles of mercury are added 
until the globules can be seen circulating through the 
pulp, and then the required amount of cyanide is 
added. After grinding this for about two hours, 10 
pounds of mixed zinc and copper amalgam are added, 
and the grinding continued four hours longer. By this 
time the precipitation of the gold from solution is very 
complete. The pulp and solution are then discharged 
into a settler, and the mercury recovered as in the 
ordinary pan process, that is, by the use of water and 
revolving stirrers. 

It was found that while one hour was sufficient to 
reduce the gold in the slimes, the sands required a 
longer treatment.- They are therefore separated from 
the slimy pulp and given a 4 days’ percolation treat- 


TREATMENT OF CONCENTRATES AND SLIMES. 133 

ment. The extraction obtained is said to be 90 per 
cent gold and 80 per cent silver, with a consumption 
°f if pounds of cyanide. The process has many dis¬ 
advantages, among which may be placed cost of 
chemicals, impure bullion, and the power required. 
The latter amounts to about 2 horse-power per ton of 
ore treated daily. 

The advantages are that the amalgam is retorted, 
and tests can be readily made in a pan at any time. 

There is considerable loss of mercury in pan amal¬ 
gamation, and it is not probable that less loss will 
occur in this treatment; this loss must be added to the 
cost of treatment. The process is practiced at the 
Santa Francisca mine, Nicaragua, and may eventually 
develop into an extremely useful method of extracting 
gold from certain ores. 

From its description and the list of chemicals, which 
are cyanide, caustic, copper sulphate, cast-iron turn¬ 
ings, zinc, and mercury, it seems to be an Arrastra- 
Patio-Boss-Freiberg-Cyanide process, and under such 
conditions the extraction should be high, if costly. 

Pneumatic Cyanide Process .—Agitation by means 
of compressed air is one of the oldest methods of 
washing phosphate rock. As a means of supplying 
oxygen to solutions of cyanide and ore it has been 
patented, but this patent does not seem valid to the 
writer, who at one time before the present patents 


134 


CYANIDE PROCESSES. 


were granted went into the subject of this process 
thoroughly. Any one has the right to agitate ore 
by compressed air, and that it supplies oxygen during 
agitation follows naturally. In order to patent com¬ 
pressed air as a means of supplying oxygen one must 
go behind the returns and prevent agitation. Never¬ 
theless there is a patented pneumatic cyanide process, 
and while it has not superseded the other processes 

it is as good as, and in some cases better than, they 
are. 

The process as outlined consists of steel vats, con¬ 
nected near the bottom by pipes, and by means of a 
tee with a pipe running over the vats. From the pipe 
running over the vat two pipes extend down into the 
tanks, in such a way that air will be forced into the 
pulp and, bubbling up, will agitate the mass. It is 
claimed that this arrangement will do in seven hours 

the leaching that formerly required from two to six 
days. 





CHAPTER X. 


ELECTRICITY APPLIED TO CYANIDING. 

Introduction.—Mr. MacArthur said that “when 
cyanide is used in combination with the electric current 
not only is there a larger expenditure of chemicals, 
but the base metals are dissolved to a large extent 
along with the gold and silver, and for subsequent 
separation involve extra expense, which is saved by 
our process.” 

Mr. Hanny, a countryman of his, says that “when 
the electric current is used the cyanide solution may be 
weaker, as its action is increased by the current.” 
He further states that “ only gold and silver salts are 
attacked by the solution, and that copper and iron 
pyrites may be stripped of their gold and not- be 
attacked otherwise. ’ ’ 

According to Berzelius, “Chemical union of any 
two substances is an electrical act; that during contact 
previous to union the one substance is relatively posi¬ 
tive, the other relative negative, and the act of union 
is a consequence of the attraction existing between the 

i35 


i 3 6 


CYANIDE PROCESSES. 


substances in these two states; also that in the act of 
uniting the two electrical conditions neutralize each 
other and produce heat.” 

As MacArthur and Forrest were the parties to intro¬ 
duce the practical application of cyanide to extraction 
of gold from ores, Siemens-Halske may be considered 
the first to introduce electricity into the process to 
assist its application. Neither of them designed or 
produced anything new, but, having faith in their 
experiments, they applied their capital to obtain useful 
results. 

When Dr. Siemens took the matter up, he found 
that electrical precipitation was equally effective with 
either strong or weak cyanide solutions. This was 
one step in the right direction, namely, a saving in 
chemicals. 

Julian Rae of Syracuse, N. Y., patented an apparatus 
as early as 1867 for the electrical precipitation of gold 
from ores, but the patent, like Simpson’s of 1885, 
seems to have been left on the shelf to mould. 
Mr. Rae did, however, make one practical test, at the 
Douglas mill, Nevada, which was not entirely satisfac¬ 
tory. His failure to obtain uniform results was due to 
his using an alternating current. Electrolysis with 
such currents must necessarily be very slow, and the 
slower the reversal of the current the better the results, 
for if the current alternates quickly there will not be 


ELECTRICITY APPLIED TO CYANIDING . 


137 


given time enough for the solution to deposit its metal 
compound before it is repelled by a reversal of the 
current. 

Wm. Crookes (patent No. 462,535, 1891) says: 
“In carrying out my combined process I take the 
gold ore, tailings, etc., and mix with them a solution 
of nitrate or cyanide of mercury, and pass a rapidly 
alternating current of electricity through the mass, 
either when at rest or agitated in any manner.” 

“ The bulk of the mass is not a good conductor of 
eletricity, while the fine particles of gold are excellent 
conductors.” “Iron or carbon can be used as elec¬ 
trodes, and each electrode is alternately anode and 
cathode.” “Assuming that sulphate of mercury is 
the mercurial salt, the current liberates sulphuric acid 
at one pole and mercury at the other.” “ The action 
now being, reversed, the mercury liberated previously 
has a molecule of acid to unite with it, so that at each 
pole the mercurial salt is decomposed only to unite 
again.” “ Since the gold in the wet mass is a better 
conductor than the surrounding mass, the equipotential 
lines of force will converge toward them, so that more 
of the current passes through them than the rest of the 
mass, and the two sides of each particle of gold act as 
anode and cathode. On one side sulphuric acid is 
liberated, on the other mercury, but the affinity of gold 
for mercury is so great that they instantly amalgamate 


138 


CY/4NIDE PROCESSES. 


on one side, finally on the other side. Thus the size 
of the particles is not essential, as the finest flour and 
float gold will be amalgamated.- Nor does it matter 
to what degree of coarseness the ore is crushed so long 
as the mercurial salt penetrates to one part of the piece 
of gold locked up in the ore, for the action will then 
take place and the metal become amalgamated.” 

“The advantage incidental to the use of an alter¬ 
nating current is that the sudden and violent decom¬ 
positions and recompositions cause the mass to become 
hot, and so greatly facilitate amalgamation.” 

The efficient action is dependent upon several 
variable factors, viz., current density, area of elec¬ 
trodes, rate of alternation per second, and electric 
conductivity of the crushed ore and liquid.” 

There is no record that this process has had prac¬ 
tical application, but there is a record made by 
Mr. Rae, who used an alternating current and mercury 
cathode, which indicates strongly that it will not be a 
success. It is mentioned here because of its connec¬ 
tion with electrical cyaniding operations. 

Electrolysis.—If a metal is in solution as a chemical 
compound, it may be separated and deposited as a 
pure metal by passing an electric current in such a 
manner that the solution acts as a conductor of elec¬ 
tricity. The essential conditions necessary for elec¬ 
trolysis are that the substance be a liquid, a definite 


ELECTRICITY APPLIED TO CYANIDING. 


T 39 


chemical compound, and a conductor of electricity. 
When aurio-potassic cyanide delivers up its gold to 
zinc as explained, it would be converted into caustic 
potash, did it not have a definite chemical composition 
of its own that could unite quickly with the zinc 
liberated. But the interchange of gold for zinc is the 
result of electrolysis, and the formation of zinc-potassic 
cyanide is a secondary product of electrolysis. In 
passing a current through a solution (which is termed 
an electrolyte) it is customary to partly submerge 
two metals in the solution. That metal by which the 
current enters the electrolyte is the anode, and is more 
or less dissolved during the operation, oxygen being 
liberated at this pole. 

That metal by which the current leaves the elec¬ 
trolyte is the cathode, and is not so badly eroded as 
the anode, although metal from the solution is 
deposited upon it and hydrogen is liberated at this 
pole. 

At the anode, also called the positive electrode, the 
solution is broken up into what are termed ions, and 
as they are charged with positive electricity they are 
repelled and move towards the negative electrode 
which attracts them. Such ions are termed anions. 

Anions when they reach the negative electrode are 
broken up and deposit their metal, while the chemical 
portion of the anion receives negative electricity and is 


140 


CY/INIDE PROCESSES. 


repelled by the cathode. This ion is termed a cation. 
The anions move directly towards the cathode, and 
the cations towards the anode, thus forming an electric 
circuit, for the transmission of the current. It is 
known that an electrical current will pass through an 
electrolyte when it is so feeble as not to cause elec¬ 
trolysis; consequently, in order to deposit a metal, there 
must be a definite amount of electricity passed. Not 
only precise quantities of current, but definite amounts 
of electrical energy, are required to separate definite 
weights of substances, and this amount of electrical 
energy depends upon the strength of the chemical 
union of the compound, upon the chemical equivalent 
or valence of the element to be separated, and upon 
the amount of the conduction resistance of the elec¬ 
trolyte. It is not misdirected currents of electricity, 
however great, that separate reducible elements, since 
from a weak solution of a potassium salt even the 
strongest current will not deposit the metal; but by 
using a cathode of mercury of small surface the metal 
has been deposited by the aid of a feeble current. It 
thus becomes evident that the energy must be intelli¬ 
gently directed. If there is an impure anode of copper 
submerged in sulphuric acid containing copper sul¬ 
phate, the anode will be dissolved and the copper 
deposited pure, while the impurities from the anode 
will fall to the bottom of the tank or be dissolved by 


( 


ELECTRICITY APPLIED TO CYANIDING. 141 

the electrolyte. It is not necessary that the anode be 
copper, any other metal will act in a similar manner, 
and be deposited, provided the solution contains suffi¬ 
cient metal salt and not too much free sulphuric acid. 

The anode of copper will be dissolved and in time 
weaken the solution unless more copper sulphate is 
supplied before that point is reached. Other metals 
than copper can be deposited from suitable solutions 
by an electric current; in fact several metals may be 
in solution and but one deposited, that being the most 
electro-negative; but in all cases the quantity of metal 
deposited will be proportional to the quantity of current 
multiplied by the time it has been flowing. 

A relation exists between the amount of metal 
deposited by a current in a given time and the atomic 
weights of the element. This is proportional to the 
atomic weight of the metal divided by its valence. 
For example, from a solution of silver cyanide in 
potassium cyanide there will be deposited 108 grams 
of silver by the same current which would liberate 
1 gram of hydrogen in a given time, or 


atomic weight 
valence 


108 

=-= 108. 

1 


Or, in the case of cyanide of gold in a solution of 
potassium cyanide (the valence of gold being 3), 



142 


CYANIDE PROCESSES. 


196.7 

y ~ 65.5C) grams of gold will be deposited in tne 

same period and with the same current that would 
liberate 1 gram of hydrogen. 

Current Strength—When one practical unit quantity 
of electricity is flowing through a conductor every 
second, the strength of the current is one ampere. It 
makes no difference in the number of amperes whether 
the current flows for a long time or only a fraction of 
a second; if the quantity of electricity that would flow 
in 1 second is the same in both cases, then the strength 
of the current in amperes is the same. 

A current of electricity in passing through water will 
decompose it into its two elements: hydrogen will be 
liberated at the cathode and oxygen at the anode. 

1 he quantity of water decomposed is proportional to 
the strength of the current flowing, and also to the time 
during which it flows. This fact has been adopted as 
the basis for a unit strength of current, that is, one 
that will decompose a certain quantity of water in a 
stated time, say 1 second. 

By universal agreement 1 ampere is that strength of 
current which will decompose .00009324 gram or 
.00143S8 grain of water in 1 second. If a current of 
one ampere flows continuously for one hour, it is 
termed an ampere-hour; if 2 or more amperes flow 
continuously, there are said to be 2 or more ampere- 


ELECTRICITY APPLIED TO CYANIDING. 


*43 


hours. The number of grams of silver that would be 
liberated in an ampere-hour may be found as follows: 

.00009324 X 3600 107.66 

- --- X -— -= 4-0264 grams. 

The number of grams of gold that will be deposited 
in an ampere-hour may be found in a similar manner, 
the ^ representing the proportional part of hydrogen 
in water according to the molecular weight theory, 
thus: 

.00009324 X 3600 196.7 

---X —— = 2.4519. 

Voltage.—In all electrical problems there are two 
properties of the current to be considered: the number 
of amperes of flow, and the volts or pressure. There 
is a definite amount of voltage for every element, and 
no current will pass through an electrolyte until this 
voltage has been reached. 

This pressure is intimately connected with the heat 
of combination or chemical affinity, and must be deter¬ 
mined for any electrolyte by experiments in the 
laboratory. 

In voltaic cells each metal of the couple is corroded 
and evolves heat; but the highest electromotive force 
is obtained by coupling two elements widest apart in 
the voltaic-tension series; that is, other things being 
equal, the most easily corroded metal, coupled with 







1 44 


CYANIDE PROCESSES . 


the one least easily corroded, yields the most intense 
current. 

The volt is the practical unit of electromotive force, 

and may be further defined as that electromotive force 

(E.M.F.) which will cause a current (C) to flow 

against a resistance ( 7 ?) of i ohm. To measure the 

amperes and volts, ampere-meters and volt-meters are 
necessary. 

The Ohm.—The resistance which the electromotive 

force must overcome to produce a current sufficient to 

flow through an electrolyte is measured in ohms , or 

the practical unit of electrical resistance. The ohm 

has several values, but the legal ohm is the resistance 

offered by a column of mercury 41.7323 inches high, 

having a cross-section of .00155 square inch, at a 

temperature of 32° F. Ohm's law is expressed as 
follows: 

Strength of current (C) — ^ ctromot i v e force (E) 

resistance (R} 

When the values of any two of these quantities are 
known the others may be found by transposing, thus: 

C = ~r■> E-CR-, and R = 

The Watt —Horse-power expressed mechanically is 
33,000 foot-pounds per minute or 550 foot-pounds per 
second. The watt is equivalent to .7373 foot-pound 





ELECTRICITY APPLIED TO CYAN I DING. 


H 5 


per second, or ~ ~ = 746 watts as an electrical 

'7373 

horse-power. The watt is also the product of amperes 

by volts, that is, W — EC , and hence W — — 

746 


electrical horse-power. 

With the elements of the electrical actions and units 
understood, the reader will be able to follow the reac¬ 
tions which must occur in electrolysis. 

The Electro-cyanide Process_The ideal electro¬ 

cyanide process should conform to the following prop¬ 
ositions : 

(a) The precious metals are to be extracted direct 
from the ores, and be precipitated in such form that 
they can be readily recovered and refined into fairly 
pure bullion. 


There .must be economy in the use of potassium 
cyanide, and it is known that under certain conditions 
there is a nearer approach to theory in the consump¬ 
tion of cyanide by the combined action of electricity 
and potassium cyanide than by cyanide and zinc pre¬ 
cipitation. 

(ft) The process should dissolve and precipitate the 
precious metals, so that the bullion may be recovered 
the same day, thereby effecting a saving in time, but 
the cost of so doing must not exceed that of ordinary 
leaching. 



146 


CYANIDE PROCESSES. 


W The Process must treat slimes, discharge the vat, 
and allow the solution to run practically free from gold 
out of the vat; in other words, the exhausted solution 
should contain less than 50 cents of gold in one ton. 

Electricity and Oxygen.—Electricity in the leaching- 
vat should hasten the dissolution of gold in a cyanide 
solution, since oxygen, the much-needed element, is 
given off at the anode. In case agitation is applied in 
conjunction with electricity there will be two sources 
of oxygen. There seems to be some question as to 
the manner in which the cyanide solution is increased 
in dissolving power by becoming an electrolyte, but it 
must be evident to the reader that such is the case, 
although somewhat surrounded by reactions not 
definitely understood. 

1 ext-books on electrolysis state that the chemical 
changes directly produced do not take place in the 
mass or body of the electrolyte but at the electrodes, 
and aie strictly limited to thin layers of metal and 
liquid in immediate contact with each other. The 
ions formed at the anode move in the direction of the 
cathode and serve as carriers of the cyanide of gold 
molecule, never being in a free state until they reach 
the cathode. In the Siemens-Halske precipitation 
process the solution is comparatively free from solid 

matter, and at the same time the anodes and cathodes 
are close to each other. 


ELECTRICITY APPLIED TO CYANIDING. 147 

The solution is allowed to pass slowly by these 
electrodes, and consequently the anions are attracted 
and the gold liberated from solution. In the Pelatan- 
Clerici process the ore and solution are in contact with 
che electrodes, which are a considerable distance apart, 
and in this process the ions cannot travel in one direc¬ 
tion on account of the disturbance caused by the 
agitator. 

It is probable that the potassium cyanide and gold 
form the double salt 2AuKCN 2 , independent of the 
electrodes, and that on coming in contact with the 
anode the potassium is liberated, the ion being AuCN.,, 
which, charged with positive electricity, goes to the 
cathode only as agitation permits. Whenever one of 
these cyanide-of-gold molecules comes in contact with 
the cathode it is immediately broken up and the gold 
deposited, while the chemical, cyanogen, is liberated. 

As the cyanogen will always find hydrogen at the 
cathode it will be converted into hydrocyanic acid, 
which cannot remain inactive, and will combine with 
the potassium hydrate to form potassium cyanide. 

It is difficult to account for the reactions which occur 
in the Pelatan-Clerici process except upon the grounds 
given. The reactions may be formulated as follows: 

In the solution 


4KCN + 2 Au + O + H 2 0 = 2AuKCN 2 + 2KOH. 


148 


CYANIDE PROCESSES. 


At the anode oxygen is given off in the presence of 
water, hence 


2AuKCN 2 + H,0 +0 = 2AuCN 2 -f 2KOH. 

At the cathode hydrogen is liberated in the presence 
of cyanogen, therefore 

2 AuCN 2 -|- 2 K 0 H-f 4 ^ — 2 Au -|- 4HCN 2KOH 
and, the gold being deposited, 

2HCN -f 2KOH = 2ICCN + 2H 2 0. 

This is the regular reaction independent of the part 
the electric current plays in hastening the process. 
If the latter acts as stated, it must be by furnishing 
oxygen for the process and then immediately convert¬ 
ing the aurio-potassic cyanide into cyanide of gold. 
Pelatan and Clerici use for an electrolyte sodium chlo¬ 
ride in order to have a freer passage for the current, 
and thereby counteract the resistance which would, it 
is claimed, take place with such a poor electrolyte as 
potassium cyanide alone. This they claim is to form 
a definite chemical compound, but, as stated, potas¬ 
sium cyanide also forms a definite chemical compound, 
besides is divisible into a great many molecules and 
still be potassium cyanide and a definite chemical 

compound, capable of transmitting an electric current 
more readily than water. 


ELECTRICITY APPLIED TO CYANIDING. 


149 


The conductivity of a solution depends upon the 
number of free ions in it; in other words, on the extent 
of dissociation; and it is known that it is a difficult 
matter to deposit potassium electrolytically except on 
a cathode of mercury of small surface. It may be 
argued, therefore, that while a weak current could pre¬ 
cipitate potassium from the solution, it will not do so 
as long as gold is present in the solution, as the chief 
amount of conduction resistance is in the electrolyte, 
and not in the electrodes, and since by a rise of tem¬ 
perature the resistance of the liquid is decreased the 
effect is to facilitate electrolysis. At the same time 
this rise in temperature should increase the solubility 
of the solution. 

The amount of energy required to separate gold 
from-aurio potassic cyanide depends upon the voltaic 
tension between potassium and gold, which is con¬ 
siderable ; hence the energy required is not great. 
The amount of energy required to separate gold and 
cyanogen is more on account of their nearness in the 
voltaic-tension series, but it also depends upon the 
solubility of the anode, for which reason an easily 
soluble anode must be chosen. 

The datum which must be known for the successful 
practice of electro-cyaniding is the percentage of gold 
to be dissolved. The amount of cyanide must be 
based upon this quantity of gold, and then the neces- 


CYANIDE PROCESSES. 


l 5 ° 

sary current calculated for precipitating the gold in a 
given time. 

Every electrolyte must be electrolyzed at a partic¬ 
ular rate in order to continuously obtain from it the 
desired quantity of metal. This latter datum can be 
obtained from a few experiments, and then tables 
computed to fit every possible case, care being taken 
to use only sufficient current to accomplish the work; 
otherwise there will be a waste of power, injury to the 
electrolyte, and a deposit of impure metal. 


CHAPTER XI. 


ELECTRODES. 

Electro-gilding has been in use over half a century. 
Dr. Wright of Birmingham, England, used gold 
cyanide solutions for electro-gilding in 1840. 

The principle is that of depositing gold from solu¬ 
tion upon a cathode of metal to be plated. 

The current or circuit is made so that electrical 
action must take place between the electrodes through 
an electrolyte. The current decomposes the liquid at 
the cathode, liberating the metal from its chemical 
combination. 

Eisner’s equation has with electrical action the same 
features that it possessed where potassium cyanide and 
zinc precipitation was employed. The oxygen decom¬ 
poses the potassium of the auro-potassic cyanide salt 
as before, except more briskly. 

In this instance agitation is not as important for 
generating oxygen as it is for moving the ore and 
liquid so that the electrolyte can come in contact with 
the electrodes, in one instance receiving life for dis- 

151 


1 5 2 


CYANIDE PROCESSES. 


solving, in the other delivering up its metal - and 
becoming regenerated, and sent on its way to dissolve 
more gold. 

With electrical action the potassium cyanide can be 
greatly reduced in the solution. As stated theoretically, 
i part of cyanide should dissolve 1.5 parts of gold, but 
practically it requires from forty to sixty times that 
quantity. 

By the aid of electricity in connection with cyanide 
the amount of the latter needed has been reduced to 
16 parts cyanide to 1 part of gold dissolved, and there 
are good grounds for belief that it will approach nearer 
the theoretical limit. 

As the solvent action takes place very much quicker, 
and as there is not the same loss of cyanide as in 
percolation and zinc precipitation, a very great saving 
in time and expense should be recorded. 

The liquid remaining after leaching will not contain 
impurities injurious to future leaching when electro- 
cyaniding is practiced. 

Agitation with an electric current passing is not as 
important as in the former practice, nor would it be as 
far as oxidation and precipitation go, but there are 
other considerations which make it desirable that the 
sludge be kept in motion. 

The solution is very weak, and in order to hasten 
its action mechanical power should be used. While it 


ELECTRODES. 


1 53 


is possible that the liberation of gases and the action 
of gravity due to different densities in the electrolyte, 
either with or without gold in suspension, would create 
circulation, still the fact is that the sludge would settle 
around and on one or more of the cathodes, thus 
hindering, if not entirely stopping, the deposition of the 
metals on the cathode. Were the liquid clear or 
filtered from the sludge, this would ■ not be the case, 
but by filtering time is lost and the cyanide cannot do 
the work as readily as it is accomplished by agitation. 

The chief objects in the use of electricity are to save 
time, cyanide, and zinc; to do away with several 
tedious filterings or percolations, as they are called; to 
do what leaching is required with one solution at one 
time; and precipitate the gold at the same time that 
the operation is carried on in the vat. To accomplish 
this the apparatus must with the solution satisfy the 
following condition: First there must be a metal anode 
not easily coroded or dissolved by the solution. The 
proper position of this anode is above the cathode; but 
it can be parallel to it if both are perpendicular. 
When horizontal and in courses, the oxides from the 
anode fall away, and being deposited on the cathode 
will interfere with its action, especially if they can 
unite chemically with it. Secondly, the cathode must 
allow the gold to adhere to it, and after the process is 
completed allow the metal to be easily recovered. 


T 54 


CYANIDE PROCESSES. 


When the gold must be dissolved from the cathode by 
acid, such sheets of thin metal as can be readily 
removed from the vat should be used ; the thin gold 
can then be removed by scraping the plates. These 
plates should also be arranged so as to be easily lifted 
out and returned to the vat, or if mercury is used 
it must be arranged to run off readily so that it can 
be strained and returned to the vat. Each inventor 
has the best mode of accomplishing these results, 

or at least did have until some one else overtopped 
him. 

As power must be used for agitation, it must be 
sufficient and applied in such a manner as to stir up 
the whole mass and keep it in motion. The anode 
being the dissolving-point and the cathode the receiv¬ 
ing-point, if the power be applied to either one, that 
is, the mechanical power for agitation, it should be 
applied to the anode. If this power can be applied to 
either electrode, matters have been simplified one step 
more by lessening mechanical complications. 

The best way to recover the precious metals is in 
the form of amalgam, if it can be accomplished. 

When considering electrodes the position in the 
voltaic-tension series is important, for if a readily dis¬ 
soluble anode is used with a cathode not easily effected 
by the current and solution, the ideal voltaic couple is 
approached; but in this case such anodes 


are not 


ELECTRODES . 


*55 


highly desirable, as they are expensive and foul the 
solution. 

It becomes necessary also to consider the cathode, 
for in some cases the metal will not adhere, in others 
it will adhere too firmly, and again it will be in such a 
powdery condition as to fall away from the cathode 
and become mixed with the sediments in the bottom 
of the tank. 

The electrodes are then matters of no little impor¬ 
tance in the electro-cyanide process. The current 
strength has much to do with the life of electrodes, for 
if more current is used than is necessary they will be 
wasted. In copper refining the electrodes are given 
the same superficial area as nearly as possible, the 
object being to afford as much dissolving as depositing 
surface, that the deposit may be uniform. In electro- 
cyaniding this is possible only where the electrodes are 
stationary, but where the movement of one of the 
electrodes occur this may not be practicable. Again, 
it is stated on the results of experiments that where 
mercury is the cathode, it should be sometimes quite 
small. The reduction in the size of either electrode is 
similar to adding resistance to the passage of the 
current, and, as von Gernet says, “a better effect is 
produced by doubling the surface of electrodes than by 
increasing the current tenfold.” 

In using an iron anode and a lead cathode for the 


CYANIDE PROCESSES. 


J 5 6 

purpose of depositing gold from a cyanide solution, it 
was found that a 5-H.P. engine yielded 3^ H.P. elec¬ 
trical energy at 4 volts pressure. This is equivalent 
to W = EC, or 

W 746 watts X 3 i H.P. 

C =^E = --= 6 5 2 '75 amperes. 

It requires a definite amount of current to oxidize a 
.definite amount of iron, and in this instance 1080 
pounds were oxidized in a month; the gold precipi¬ 
tated in that time was 335,935 grains in 700 hours, or 
4709 grains per hour. According to the gold ampere- 
hour of 38.1 grains it requires 8817 ampere-hours 
to deposit this amount, but 210,000 ampere-hours 
were expended or 201,283 more ampere-hours 
than were required. The current necessary to deposit 
this amount of gold was 12.6 amperes, hence the 

12.6 

efficiency of the current was —-— = 4.2 per cent 

300 * ’ 

because 300 amperes were actually used. The re¬ 
mainder of the current was wasted energy, and was 
expended upon the iron, which diluted the electrolyte 
by forming Prussian blue, as well as being dissolved. 

There must be a certain amount of energy, but not 
too much. The amount should be determined for the 
work to be performed. If to-day a two-ounce gold 
ore is to be treated in ten hours, more amperes will be 






ELECTRODES. 


157 


required than if a one-ounce ore were to be treated 
to-morrow in the same time, and the oxidation of the 
anode will not be more, since surplus energy has not 
been expended upon it. 

As stated, the electrodes should be as nearly of a 
size as possible when uniform results are to be obtained. 
They should be, especially the anode, of a metal or 
substance not easily acted on by the solution; iron 
seems to be suitable to fulfil the conditions of the 
anode, as it is not readily acted upon by the solution, 
and when oxidized it is due in great measure to having 
the current too energetic for the work in hand. 

The question of the size of anodes and cathodes, 
that is, the surface exposed where agitation is used, 
especially iron and mercury, is purely theoretical. 
The anode in some cases is not more than one third 
the surface of the cathode, and yet the iron anode is 
not very materially oxidized. This may be due to the 
movement of the anode, which rotates horizontally over 
the cathode of mercury, but at some distance from it. 
However, it does not seem possible that this rotation 
has much to do with it, since the current is continuous, 
and the voltmeters and ampere-meters do not show 
any variation of importance. One would suppose that 
energy would be expended more upon this small 
anode, but practice shows it is not. 

The electrolyte seems to be a good conductor of the 


CYANIDE PROCESSES. 


158 


current, and not being often in a state of a metallic 
ion on account of gold being so widely distributed, 
nevertheless it conducts the current, when propor- 
tioned rightly for the work, to the anode and cathode, 
fairly well. While the heat arising from conduction 
resistance throughout the electrolyte naturally reduces 
the resistance, it is small, and that leads one again to 
presume that potassium cyanide with pulp is a fairly 
good conductor. The quantity of energy lost by the 
corrosion of the cathode is very small. 

The electrolyte must be a liquid, a definite chemical 
compound, and a conductor of electricity. It is con¬ 
sidered in electrolysis that an electrolyte must have a 
constant composition, whereby the proper working 
conditions may be constantly maintained; in other 
words, to make gold deposition by electricity prac¬ 
ticable, there should be a soluble gold anode. This 
point is not well taken, for the process has been worked 

satisfactorily day after day with a weak gold solution 
and an iron anode. 


It is true the electrolyte is changed chemically by 
the passage of the current, but in any case the potas¬ 
sium and cyanide remain in some form in the solution 


It is true that the electrolyte may offer a high specific 
resistance; but it is more than likely that impurities 
m the liquor assist in a measure the passage of the 
current, or they may be introduced artificially to assist 


ELECTRODES. 


1 59 


it, as, for instance, in the Pelatan-Clerici process, 
about i per cent of common salt (NaCl) is placed 
in the bath, for no other purpose than to give the 
electrolyte a sufficient and practically constant con¬ 
ductivity during the whole operation. If other im¬ 
purities in the liquor assist the passage of the current, 
so much the better; if they retard it, their effect is not 
noticeable. 

With such a feeble current as is generated in the 
zinc-boxes the strength of the cyanide solutions is of 
considerable moment, but when electricity is applied 
to weak cyanide solutions the strength of the solution 
is of very little moment. 

The potassium cyanide is separated into an acid and 
a base by the current, the electromotive force necessary 
to produce decomposition being much less than that 
to set free the alkali metal.* If the theory advanced 
be correct, and it evidently is from a scientific stand¬ 
point, there is KCN regenerated as soon as the gold 
is deposited, and this has the effect of keeping the 
electrolyte in good condition for the passage of the 
current irrespective of the addition of salt. Again, 
instead of a soluble anode of gold there is gold in the 
solution being dissolved, and this in a measure takes 
the place of a gold anode, especially when broken up 
from the aurio-potassic cyanide salt to aurio cyanogen. 


* Journal Chein. Soc. 1882, vol. xliii. pp. 260, 283 






CHAPTER XII. 


THE CURRENT. 

Professor Bunsen stated “that electrolysis in all 
operations marked a great # advance on chemical action 
pure and simple,” but he should have added that the 
value of any metallurgical process depends upon the 
size of the dividends. 

The cost of the current has much to do with the 
installation of an electro-cyanide plant. In some 
instances where water-power is available the cost will 
be merely nominal, but where fuel is high for generat- 
ing steam the cost will be an item of importance. 

The quantity and energy of current required for the 
electro-cyanide process are variously stated, in one 
case a current of 0.05 amperes per square foot of 
cathode surface being sufficient with 7 volts, or the 
equivalent of 5.7 H.P. for a cathode surface of 12,000 
feet. This should deposit 1471.14 grams per hour. 
In another case 0.35 ampere per square foot was suffi¬ 
cient with 5 volts pressure to carry on the operation 
with 60 feet of cathode surface. This is equivalent to 
1 H P., and should deposit 51.49 grams per hour. 


THE CURRENT. 


161 


It is only possible to obtain the amperage and 
voltage necessary for a given electrolyte by experi¬ 
ment, but after a series of experiments a table may be 
calculated based upon the quantity of gold to be dis¬ 
solved in a given time. Suppose there are 32 grams 
of gold per ton of ore and 64 grams of silver per ton 
of ore in a charge of 10 tons, and it is desired to pre¬ 
cipitate this in ten hours, it will require 


and 


320 

2.4519 x 10 


1 3 amperes for gold 


640 

4.0264 X 10 = 15 amperes for silver - 

Adding the two together gives the number of amperes 
per hour required theoretically; in practice, however, 
it is well to double this number. It is also well to 
verify this in order to find out that the amperes are not 
too high for the anode, as the number of amperes 
should not exceed 3 for each square foot of anode 
surface; should it be more, it would be better to 
lengthen the time of precipitation or use a smaller 
quantity of pulp. 

Voltage.—The voltage in any case should not be 
less than three, but the exact number can only be 
found by experiment. It is a good plan to examine 
the connections often, at least once a week, testing the 
resistance of the wires, cathodes, and anodes. 





162 


CYANIDE PROCESSES. 


It is also a good plan to have a dynamo which can 
give 2 or 3 volts more than the number calculated, for 
probably there will be a loss of potential equal to that 
number. 

Calculation of the Wires.—The formula is derived 
from Ohm’s law and is 

cla 


in which s represents the cross-section of the wire; 
/, the total length in meters; a , the number of amperes; 
v > the loss potential (2 volts); c y the coefficient of 
resistance, which for copper is .00018. The section .y 
is in square millimeters. 

The quantity and the energy of current required for 
the electro-cyanide process of dissolving gold and 
silver from their ores are variously stated. 

If in a fixed time a given electric current will deposit 
a certain quantity of metal, it will be in direct propor¬ 
tion to their electro-chemical equivalents. “ This law 
holds good only for solutions strong in metal; but with 
the dilute solutions used in the cyanide process the 
current does not find sufficient of the metallic com¬ 
pound piesent at the electrodes, and consequently 
decomposition of the water takes place. For the 
purpose of making the efficiency of the precipitation as 
great as possible constant diffusion of the solution is 
requisite.” (Von Gernet.) 



THE CURRENT . 


163 

Cost of Electric Cyaniding—To decompose gold salts 
and deposit gold requires theoretically 0.4 of a volt, 
but owing to various resistances to be overcome assume 
that it is 7 volts when a gold anode is not used. 

A current of 7 volts and 500 amperes represents 
about 4.6 H.P., costing, say, $1.84 per day of twenty- 
four hours. This current, in a solution for gilding 
purposes, where the whole of the amperage is used to 
precipitate the gold, would deposit 2.4519 x 500 = 
I22 5-95 grams per hour, which, reduced to penny¬ 
weights, gives practically a deposit of $780 in gold per 
hour, 01 $18,720 per day. The cost of electricity 

consumed would therefore not be more than 1 of 

r 8 0 0 0 

the value of the gold. If, in order to precipitate gold, 
zinc is used, there will be a consumption of 1.39 
pounds pei ounce of gold recovered, costing, according 
to Bosqui, 18.4 cents. To precipitate with electricity 
780 pennyweights of gold as in the above case for 
comparison, the cost would be $71.76. 

In the Siemens-Halske process the consumption of 
lead amounts to 3 cents per ton of tailings containing 
8 pennyweights of gold, or about 8 cents per ounce of 
gold deposited, or $23.40 in comparison with $71.76 
for zinc. The total cost of precipitation by the 
Siemens-Halske method would be $23.40 -f- $1.84 = 
$25.24, irrespective of the reduction in cost of refining 
the bullion. With the Pelatan-Clerici process the cost 


164 


CYANIDE PROCESSES. 


would be more marked, because the cost of depositing' 
includes a reduction in cost of leaching and precipita¬ 
tion; in other words, when considering $1.84 as the 
cost of precipitation, the cost of agitation is included, 
as practically none of the cathode is lost when the 
work is properly conducted. 

The cost of anodes in the above instance has not 
been included, but it is less than 1 cent per ounce of 
gold recovered. 

Objections to Electro-cyaniding.—Naturally there are 
objectionable points to electro-cyaniding, some of 
which are well taken, while others are more imaginary 
than real. Among the objections is the formation of 
ferrocyanhydric acid, which might assimilate with 
aurocyanhydric acid. One of the essential character¬ 
istics of ferrocyanides is that by adding to them a salt 
of another metal the iron is not displaced and no 
cyanide of iron is separated; hence it matters little 
about aurocyanhydric acid, as it will not be assimilated 
by ferrocyanhydric acid and can be gotten rid of by 
using a sufficiently strong current. 

The case is different with the double salt of cyanide 
of gold and potassium, and for aurocyanyhdric acid, 
since chloride of mercury separates the gold; silver 
nitrate precipitates the gold entirely, and mercury, 
lead, and zinc act partially in the same manner, 
namely, by substitution. 


CHAPTER XIII. 


ANODES. 


Platinum Anodes.—Julio H. Rae patented the use of 
a platinum anode in 1867. This metal offers great 
resistance to the passage of an electric current, conse¬ 
quently is objectionable on account of the electromo¬ 
tive force required and also its great cost. Owing to 
the fact that decomposition must take place at the 
anode of the electrolyte, energy is expended not on 
the work, but in setting free oxygen that will probably 
decompose the electrolyte, particularly if it is potassium 
cyanide. . The amount of platinum which should be 
liberated in an ampere-hour is 


196.7 

4 


X 


.00009324 

-— X 3600 = 1.835 grams, 


or about three fourths as much as gold. Other inven¬ 
tors do not coincide with Mr. Rae in suggesting this 
metal as an anode, due more probably to its cost, which 
would be exceedingly great in a plant of any size. 
Carbon Anodes.—In the Siemens-PIalske process 

carbon was experimented with for anodes, but since it 

165 





i66 


CY/INIDE PROCESSES . 


could not withstand the action of the current it was 
abandoned. 

Carbon is suggested by Malloy’s process, patented 
in 1884 and 1886. In this case, as with platinum, 
oxygen escapes. The carbon is, however, practically 
unacted upon chemically, but the current or the 
oxygen mechanically disintegrates the carbon, and 
the stronger the current the more rapid the disintegra¬ 
tion becomes. 

It is further objectionable because of loss in cur¬ 
rent, energy, and possibly the active energy of the 
electrolyte. 

Eissler in speaking of the Siemens-Halske process 
says: “Carbon could be used as an anode, but will 
not stand the action of the current, and soon crumbles 
into a fine powder which decomposes cyanide.” 
“This finely divided carbon is in suspension, and 
cannot be removed from the solution by filtration.” 
On the other hand, Mr. Weightman used arc-light 
carbons for six months, and they were at the end of 
that time in good condition. Mr. Weightman’s obser¬ 
vations do not agree with Mr. Eissler’s, but that is not 
due to error on either side. One undoubtedly had 
reference to porous carbons while the other had refer¬ 
ence to dense compact carbons coated with copper. 
The copper coating was of very great assistance even 
to the compact carbon in counteracting disintegration 


ANODES. 


167 


by the current. The great objection to carbon is its 
lack of conductivity; if silver be 100, then carbon as 
graphite is .069, and as gas-coke .038. A dis¬ 
advantage in its use is its small power of dissolution, 
which is but 1.74 ampere-hours; hence it could cause 
little deposition without great electrical energy. 

H. R. Cassel used carbon rods as anodes, as did 
Fischer and Weber (patents 1883, 1885, and 1887). 
J. B. Hanney used a mixture of plumbago and resin 
as anode, and, as he claims, with very good effect. 
As a rule, the anodes in the various processes have 
been varied but little, but in some patents they have 
been differently arranged, so as not to conflict. 

Zinc Anodes.—d he rate of dissolution of zinc by an 

electric current is ^ X _ °°^ 932 4 x 36oo _ 2 42 ^ 

grams per ampere-hour, or about the same as gold, 
and, being quite electropositive, would make an excep¬ 
tionally good anode from an electrical standpoint but 
an exceedingly bad one from an electrometallurgical 
view. 

Zinc as an anode has serious defects, in fact as 
numerous as when used as a cathode. It forms a pre¬ 
cipitate of cyanide of zinc in the solution; also zinc 
oxide on its surface, which offers resistance to the 
electromotive force, making it expensive. Should it 
precipitate on the cathode, it will also cause future 



i68 


CYANIDE PROCESSES. 


annoyance. One of the advantages claimed for elec¬ 
trolysis is that it does away with zinc impurities, 
should zinc be considered at all in connection with 
electrolysis, the process will have gone backward 
instead of forward. 

Zinc will cause the solution and deposition of 18.95 
grains in one ampere-hour; hence it is only slightly 
better than iron as a conductor, while very much 
inferior as far as by-products from the operation are 
concerned. 

Iron Anodes.—The rate of dissolution of iron by an 



electric current is — X 

4 


.596736 


grams per ampere-hour. Wrought iron and steel 
anodes when not high in carbon are more readily 
oxidized than cast iron, and form Prussian and Trum¬ 
bull's blue in a bath of potassium cyanide. 

Iron has, however, been adopted as an anode 
because of its cheapness, and because of its being little 
acted upon by cyanide of potassium solutions. While 
iron might be improved upon if cost were not an item, 
it is a difficult matter to find a substitute which may be 
handled and obtained so economically at present. 

It would be of very great assistance in a discussion 
of this kind if data similar to that of copper refining 
by electrolysis were available, but there are no such 
data. In the Pelatan-Clerici process, the anode is 






ANODES. 


169 


steel boiler-plate, about one third the size of the 
cathode, which is 60 square feet. Because of the 
revolving motion of the anode a larger size is not 
deemed necessary. In the Siemens-Halske process 
the anodes have one seventh larger surface area than 
the cathode and are of cast iron. 

The anodes in the Pelatan-Clerici process are from 
4 to 4^ inches away from the cathodes; in the Sie¬ 
mens-Halske process there are 1^ inches between the 
anode and the cathode. 

In the Moebius process of electrolytic silver-refining 
the anode and the cathode are not over inches 
apart, and precipitation is rapid. 

That the Pelatan-Clerici anode is too small would 
be the natural conclusion were it not that under the 
management of Mr. Clerici the percentage of recovery, 
with favorable conditions, was as great as that of the 
Siemens-Halske process. 


CHAPTER XIV. 

CATHODES. 

Cathodes for the electro-cyanide process are as 
important as anodes, as upon them the metal from the 
solution is to be deposited. 

The cathode must be plated with metal in such a 
manner that recovery from it will not be difficult. 
Some cathodes will not allow the gold to adhere; some 
will convert it into amorphous powder; others will 
cause it to curl up and fall away; consequently the 

choice should be one which will permit the metal to 
adhere. 

1 he cathode must be a good conductor of electricity 
and not easily corroded by the solution, although as 
a rule coatings are less frequent on the cathode than 
the anode; still there is apt to be some, and that, 

with the hydrogen which adheres to it, will diminish 
the current. 

The density of the current will regulate the deposi¬ 
tion of the metals, also the form in which they are 

170 




CATHODES. 


1 7 1 

deposited. With compound substances the cathode 
should be of such a nature as not to unite readily with 
the secondary products of electrolysis. From an 
impure solution the least electro-positive metal should 
be deposited upon the cathode first; consequently with 
a solution containing gold and potassium cyanide, 
silver and potassium cyanide, as double salts of 
cyanide, the order of deposition would be silver, gold, 
potassium; but it is doubtful under these conditions 
whether it is necessary to use a current more than 
sufficient to liberate the gold and silver, allowing the 
KCN to remain in solution undisturbed. If this can 
be accomplished, there will be considerable voltage 
saved as well as cyanogen. 

It is known that an electrical current will pass 
through an electrolyte when it is so feeble as not to 
cause electrolysis, and that aqueous solutions of the 
zinc and copper cyanides will dissolve and deposit 
equally on passage of suitable current. So one is led to 
infer from these phenomena, since the electromotive 
forces of zinc and copper are equal, that the least 
abundant metal will deposit least; but if equally solvent 
in the solution, the least electropositive will deposit 
first, and this latter has been proven in the case of 
silver salt in copper solution, and is the case in potas¬ 
sium cyanide solutions containing gold and silver. 
The size of the cathode should be larger than the 


172 


CYANIDE PROCESSES. 


anode if its conductivity is less, but may be smaller if 
its conductivity is greater. It should be of sufficient 
size, however, to be able to absorb or receive as much 
metal as is offered for deposition. 

Copper-plate Cathodes.—Copper plates as cathodes 
for gold are not a success, because gold either adheres 
too firmly and is difficult to remove, or it does not 
adhere at all. These conditions depend upon the 
strength of the current. Sheets of copper coated with 
mercury have been used, but, owing to the action of 
the cut rent, the mercury penetrates the copper, form¬ 
ing a dry amalgam which does not adhere to the 
plate. This latter objection may be overcome by using 
considerable mercury and recovering the amalgam 
after each operation. 

Should an amalgamated copper plate be placed in a 
vat with the amalgam dry on it, the chance of its 
being scraped off by abrasion or grinding of the ore is 
possible, especially if the mercury be small in amount 
and the pulp circulating strongly. The electrical cur¬ 
rent, together with the adhesion of the mercury to the 
copper plate, keeps the gold in contact with the plate. 
If too much mercury be used, it will be forced into a 
free state, but if enough is used to keep the amalgam 
plastic and no more, it will not be rubbed off. How¬ 
ever, to avoid such chances as these mercury in large 
quantities is poured into the vat to act as a cathode. 


CATHODES. 


173 


The action of the liquid in circulating may give this 
liquid mercury a movement, but as it is denser than 
the liquid it only partially assumes motion. Still it is 
sufficient, where horizontal circular motion is employed, 
to move the mercury, so as at times to uncover the 
bottom of the vat in places. Just at this point mercury 
cathodes fail, for the molecule in the act of depositing 
its atom of gold may hit a bare spot and the next 
moment be lifted away. To overcome this difficulty 
a copper amalgamated plate can be used in connection 
with the mercury, then if the liquid mercury is dis¬ 
turbed the atom of gold may be deposited on the 
copper plate. Other cathodes besides mercury and 
lead have been tried, such as carbon. 

The vat of the Pelatan-Clerici process contains 60 
square feet of copper cathode, on which is poured 500 
pounds of mercury. The mercury should amalgamate 
the coarse gold, and also the deposited gold from 
the electrolyte. The current from the anode seems 
to focus, like the heat-rays from a lens, upon that 
portion of cathode directly under the pendent stirrer- 
shaft. 

In this case the copper is penetrated, and, while not 
a decided objection, requires more time to recover the 
gold, and also demands renewal of the copper plates 
from time to time. 

It has been ascertained from experiment that 12 


1 74 


CYANIDE PROCESSES. 


square feet of cathode surface is sufficient for the 
deposition of i gram of gold in one hour. 

Lead Cathodes—The cathode of lead that is used in 
the Siemens-Halske process is of thin sheet metal, and 
is as light and thin as can be handled. It is in fact 
lead-foil stretched on iron wires, fastened to a wooden 
frame to keep it taut and offer an even, smooth surface 
for the deposit of gold. The advantages of this lead- 
foil are cheapness, light weight, hence cheap handling, 
and the recovery of gold, for in the latter case the lead 
and gold are smelted together, and the gold is re¬ 
covered by cupellation. 

Siemens and Halske have made two great improve¬ 
ments over the old leaching process in that they have 
reduced the cost and obtained purer bullion. 


I 


CHAPTER XV. 


SIEMENS-HALSKE AND PELATAN-CLERICI 

PROCESSES. 

THE SIEMENS-HALSKE PROCESS. 

The distinguishing features of this process are the 
dilute solutions used for gold extraction, and the 
precipitation of the gold from these solutions. The 
strong solution is o. I per cent and the weak solution 
o.oi per cent. In the treatment of slimes 0.008 per 
cent solutions are used at the Crown Reef South 
Africa works as the strongest, and zinc would not 
precipitate gold from such solutions satisfactorily. 

The plant and operations for this process are the 
same as for the regular cyanide process until the pre¬ 
cipitation part of the operation is reached. The 
process has been used with success at a number of 
plants in South Africa. On account of the small quan¬ 
tity of gold in solution, constant diffusion of the solu¬ 
tion is required, and this is accomplished by having a 
small but steady flow of the liquor through the pre¬ 
cipitation-boxes. The electrodes must have a large 

175 


176 


CYANIDE PROCESSES. 


surface, since their action is more efficient when this is 
the case than are small surfaces with increased current. 

The advantage claimed for this process is that a 

weak solution, say .03 per cent cyanide, will dissolve 

gold as effectively as a solution containing 0.3 per 

cent, thus saving in cyanide, but this will require a 

longer time and zinc precipitation would not be as 

effective as where electrical precipitation is practiced. 

Again, precipitation acts independently of the quantity 

of cyanide or caustic alkali in the solution, the limit of 

dilute cyanide solutions being such that they will dis- 
solve gold. 

Another feature is that precipitation will be as 
effective with acid, alkali, or neutral solutions, and 
no complications arise from the formation of lime, 
alumina, or iron hydrates. 

With copper in the ore the extraction of gold will 

be the same, but on account of the weak solutions the 
loss of cyanide will be less. 


The Precipitation-boxes. —There are four precipita¬ 
tion-boxes, constructed of wood, each 18 feet long, 
7 feet wide, and 3 feet deep. Each box contains 
eighty-nine iron-plate anodes, 7 feet by 3 feet by £ inch 
thick, encased in canvas to retain the Prussian and 
Trumbull blues produced; and eighty-eight cathodes 
of lead-foil, stretched on iron wires fixed on a wooden 
frame. Each frame contains three strips 3 feet by 


SIh MENS-HALSKE AND PEL ATAN-CLERICI PROCESSES. 177 

2 feet, so that, counting the double surface of each lead 
sheet and the number of boxes, there are 12,000 square 
feet of cathode surface and 14,000 square feet of anode 
surface. Copper wires are fixed along the top of the 
sides of the boxes to convey the current from the 
dynamos to the electrodes. 

In order to assist the circulation of the solutions, 
some of the iron sheets extend down to the bottom of 
the box, while the next are raised an inch or two 
above, thus forming a series of compartments similar 
to those shown in the zinc-boxes, where the solution 
passed in at the bottom of one box and over the top 
into the next. 

The boxes are opened once a month for a general 
clean-up. The frames carrying the lead cathodes are 
removed one at a time, and the lead sheet, which con¬ 
tains fiom 2 to 12 per cent of gold, taken from the 
frame. A fresh sheet of lead is placed on the frame 
and it is returned to the box, the whole operation 
requiring but a few minutes, during which time the 
process of precipitation continues on the lead sheets 
remaining in the box. 

The details of the process, as far as lixiviation is con¬ 
cerned, do not differ much from regular cyanide plants, 
except as stated, in using much weaker solutions. 

In speaking of this electrolytic cyanide process 
Mr. A. von Gernet stated before the South African 


i ?8 


CYANIDE PROCESSES. 


Metallurgical Society that the output from them was 
larger in profanity than in gold; since then changes 
in conditions have increased the output of profanity 
against South African gold more than fool electrolytic 
cyanide processes. 

THE PELATAN-CLERICI PROCESS. 

The Tank.—The bath is a common wooden tank 9 
feet wide and 4 feet high of from 2J to 3 tons capac¬ 
ity. A copper plate lies in the bottom of it and is 
connected with the staves by a rim so as to prevent 
any leakage of quicksilver. The copper plate is amal¬ 
gamated and covered with a thin layer of quick¬ 
silver, and is connected with the negative wire of a 
dynamo. 

The pulp in the tank is kept in motion by a four¬ 
armed agitator suspended by two collars and driven 
at the top by bevel-gearing. Several brackets break 
the vortex produced by the agitator, pushing the pulp 
to the centi e so that the pulp has an equal density in 
all the parts of the tank. The anode plates are sus¬ 
pended underneath the arms of the agitator and are 
connected with the shaft by a strong spider; the sur¬ 
faces of contact are very large and there is practially 
no resistance in the connection. The anode arms are 
from 3 to 6 inches above the quicksilver level, accord- 


SIEMENS-HALSKE AND PELATAN-CLERICI PROCESSES. 179 

ing to the kind of treatment followed and which 
depends upon the character of the ore. The shaft of 
the agitator carrying the current to the anode is con¬ 
nected with the positive pole of a dynamo by means 
of a collar slightly pressed against the shaft by a 
spring. 

Working of a Pelatan-Clerici Tank.—Treatment by 
the Pelatan-Clerici process consists of a single opera¬ 
tion. The tank is filled with crushed ore, then a dilute 
solution of cyanide of potassium, common salt, and, 
if required, some other accessory chemical is added, 
the proportion of each one being calculated accord¬ 
ing to the quality of the ore treated. The agitator is 
next set in motion so as to mix the ore with the solu¬ 
tion and to make a liquid sludge through which the 
current is allowed to pass freely. 

When the ore has remained sufficiently long in the 
vat under the combined influence of the agitator 
and current, so that the gold and silver have been 
deposited as amalgam, the solution and the tailings 
are removed through an opening at the bottom. The 
tank is then ready to receive another charge of ore. 
Where water is scarce the pulp is allowed to settle in 
a tank below the vat, the liquid drained off and 
pumped up into the treatment-tanks. Even if the 
liquid is not clear and but contains very fine material 
in suspension that does not detract from its further 


i8o 


CYANIDE PROCESSES. 


use, because the process works even better with very 
fine slimes than with coarser stuff. 

The time required for working out a charge varies 
from eight to twelve hours. 

The cost of labor is small, as nearly all the hand 
work is reduced to opening and shutting a few valves; 
but a very close supervision is necessary. There are 
no parts which are specially liable to rapid wear and 
tear. 

Dissolution.—The tank is divided into two parts by 
the anode plates. In the lower part the precipitation 
takes place when the dissolution is completed in the 
upper part. This division is not very correct; accord¬ 
ing to the theory that all the liquid between the 
anode and the cathode is electrolyzed, it is not pos¬ 
sible foi dissolution to take place in the lower part; 
but according to the theory that only the liquid in 
contact with the anode and cathode is decomposed, 
it is possible to have some dissolution in the lower 
part. 

The current decomposes the potassium cyanide first 
into fiee cyanhydric acid and metallic potassium; the 
free cyanhydric acid is diffused as statu nascendi in the 
bath, but it cannot reunite with gold and silver in the 
lower part of the bath, because the current passing 
through does not allow the chemical combination, so 
that both gold and silver combine with free cyanhydric 


SIEMENS-HALSKE AND PELATAN CLERICl PROCESSES. 181 

a.cid only in the upper part of the tank. At the same 
time a small amount of both gold and silver is dis¬ 
solved in the cyanide of potassium. Free oxygen in 
the bath, liberated by the current, helps the dissolu¬ 
tion of gold and silver in the cyanide of potassium, 
as is proven by the Kendall process which uses per¬ 
oxide of sodium for the purpose. 

But, notwithstanding this, the largest amount of 
gold and silver is dissolved by the free cyanhydric 
acid, for the latter, especially at statu nascendi , is a 
stronger solvent than the potassium cyanide, as is 
proven by the fact that in the Pelatan-Clerici process 
the dissolution of all the gold takes place in four or 
five hours, while it never takes less than twenty-four 
hours in the common cyanide process. 

The current after a short time begins to decompose 
the double * cyanide of potassium and gold and the 
cyanides of gold, silver, and potassium, and when the 
cyanhydric acid produced is ready to dissolve more 
gold and silver, the gold begins to be deposited. 

Gold and silver which are sometimes in a coarse 

4 

condition, would require a long time to be dissolved, 
but the Pelatan-Clerici process acting in such cases as 
a common amalgamation-pan, by holding the pulp 
suspended in the liquid solution permits the coarse 
grains of gold and silver to gradually sink to the 
bottom of the vat, where they are amalgamated. 


182 


CYANIDE PROCESSES. 


Advantage is take of the cyanhydric acid liberated 
at the anode, so that the solving of the gold con¬ 
tinues and aids in keeping the electrolyte constant for 
a certain time. 

Precipitation. —The Pelatan-Clerici process is some¬ 
times misunderstood, because it is compared with 
electroplating and some other electrical processes. It 
is true that there is electrolytic precipitation, as in 
the other processes and electroplating, but the precipi¬ 
tation is obtained in such a different way that a simile 
is not possible. 

In the Siemens-Halske process diffusion is necessary; 
in this process and in electroplating the current den¬ 
sity must be calculated so that the deposit is regular 
and neither crystalline nor pulverulent. The exhaus¬ 
tion of the salts near the cathode is also a cause of 
imperfect deposits in electroplating. 

The nature of the deposit does not interfere in the 
Pelatan-Clerici process, because the variations of 
density and intensity of the current do not change the 
physical conditions of the molecules, but the actions of 
the molecular force. The setting free of hydrogen, 
notwithstanding the increased number of amperes 
required, is a great advantage, the hydrogen keeping 
the quicksilver clean. 

The conditions of precipitation do not require 
soluble anodes of deposited metal, concentrated solu- 


SIEMENS-HA LSKE AND PEL AT AN CLERICI PROCESSES. 183 

tions, nor yet an electrolyte of constant composition, 
and it is more than likely that some of the impurities 
in the liquid assist or retard the action of the current, 
but the effects of these compounds may be prevented. 

With purely chemical reactions it makes consider¬ 
able difference to the ordinary cyanide process whether 
the solution is strong or weak; and as far as the depo¬ 
sition of metal is concerned it is possible to use 
so weak a solution of cyanide that the finest zinc 
shavings will not deposit the gold, while an elec¬ 
trical current of determined intensity and density 
readily deposits it. 

It is frequently stated to be impossible to exhaust 
the solution by electrolytic deposition, and that is 
true; but when it is possible, as in the Pelatan-Clerici 
process, to have the solutions carry fractions of grams 
after eleven hours’ run (usually less than J gram 
per ton of ore) one may say the solutions are practi¬ 
cally exhausted. 

The chief factors for perfect deposition are strength 
of the counter E.M.F. to be overcome, the chemical 
equivalent of the substances to be separated, the con¬ 
duction-resistance of the electrolyte, and the selective 
electrolytic action of the current. 

The action at the anode regulates the deposition of 
the metals, as stated by Becquerel’s law, and the 
salts are decomposed in the order stated by Tom- 


184 


CYANIDE PROCESSES. 


masi s law; that is to say, the order of decomposition 
of the salt is regulated by the amount of E.M.F. re¬ 
quired. To this last law may be added that the order 
of the decomposition of salts is regulated by the de¬ 
gree of weakness of the solution. 

Thus the salt which opposes the less counter E.M.F. 
is decomposed first, and the salt which is next in order 
of amount of E.M.F. required begins to be decom¬ 
posed when the solution of the first salt has reached 
a determined degree of weakness, etc.; and the same 
for the following salts. 

In this way there may be several salts decomposed 
at the same time, but the degree of exhaustion of the 
solution of each salt will be indirectly proportional to 
the required E.M.F. 

In a fixed time a given current will deposit a certain 
quantity of metal, but in a dilute solution the current 
does not find sufficient metal present to decompose it, 
therefore decomposes water. 

This latter decomposition raises the temperature, and 
in so doing assists in solving gold, in keeping warm 
the quicksilver, increasing its absorption capacity with¬ 
out increasing the temperature, sufficiently to cause 
either extra appreciable resistance to the current or 
an appreciable destruction of cyanide. 

The highest specific resistance, which robs the elec- 
trolytical deposition processes of their cheapness, 


SIEMENS-HA LSKE AND PEL AT AN CLERICI PROCESSES. 185 

scientifically taken advantage of as in the Pelatan- 
Clerici process, aids in simplifying the process. 

The theory of Prof. Christy is that in the electro- 
lytical precipitation the AuCN 2 goes to the anode, and 
the metallic potassium to the cathode, or under ordi¬ 
nary conditions gold is deposited upon an iron anode. 
If the salt of gold and potassium is decomposed, the 
gold must be found on the cathode; it is much more 
probable that the KCN 2 goes to the anode and gold 
to the cathode, because gold is less positive than 
potassium. 

Electrical precipitation, especially when the theory 
is not well understood and imperfectly applied, is not 
perfect, but electrical precipitation is embodied in the 
process with evident success. 

In the cut shown of the Pelatan-Clerici vat the 
anode is seen to be a four-bladed propeller fastened to 
a shaft depending from a gear-wheel. In the anodes 
are seen a number of wooden teeth which extend to 
within 1J inches of the cathode. These teeth are for 
the purpose of keeping the sands from settling on the 
mercury. In one instance on record they were placed 
so low that the amalgam and mercury had to be col¬ 
lected in the creek bed, scarcely any remaining in 
the vat. The current is seen to enter the shaft by 
a wire, and leave the vat by a wire attached to the 

cathode. 


186 


CYANIDE PROCESSES . 


In practice there are two of these vats, one slightly 
above the other, the ore having a preliminary treat¬ 
ment in the first vat, and being cyanided in the 



Fig. 12 

second. The method of moving the stirrer in the vat 

is so plainly shown that it needs no further explana- 
tion. 































































































CHAPTER XVI. 

GENERAL INFORMATION ON CYANIDING. 

In all mill work uniformity of product is desirable, 
but particularly is this the case in metallurgical work, 
to obtain the most satisfactory results. Of the two 
methods of crushing or stamping in use, namely, the 
wet and the dry, the wet has given the better results 
both in regard to uniformity of the grains and speed of 
crushing. 

When wet crushing is practiced water is allowed to 
flow into the mortar of the stamp-mill and flow out 
through a screen. The size mesh used on these 
screens varies from sixty to one hundred for amal¬ 
gamation, but for the cyanide process it has been in 
many instances possible to use 30-mesh screens and 
even very much coarser. 

The size of the mesh of the screen determines the 
degree of fineness to which crushing is to be carried, 
as all fine particles which can pass the mesh are carried 
through by water, while all that cannot pass through 
remain in the mortar to be reduced in size until they 
can. 

187 


CYANIDE PROCESSES. 


188 

One of the obstacles to wet stamping is the quantity 
ol w atei necessary to do the work of uniform crushing. 
1 liis w atei has been in some instances returned from 
settling-tanks back into the mortar to be used again 
and again. While there are no objections to the use 
of this water, there are to pumping it. It is under¬ 
stood that with wet crushing water enough must be 
used to allow the sludge to flow through the screens. 
It is often to the advantage of the cyanide process that 
coarse crushing is allowable, both in regard to water 
used and time saved in crushing; still even this time 
advantage is sometimes more than counterbalanced 
by time lost in leaching with the cyanide solution 
when coarse crushing is practiced. For where time is 
saved in crushing, and subsequent drainage of water, 
the cyanide solution in some instances must remain 
longer in contact with ore being treated. 

On the other hand, when fine crushing is practiced 
the water drains slowly from the settling-tanks, leav¬ 
ing the fine ore sometimes so firmly packed, if clayey 
or slimy, as to allow of almost no filtration, even when 
suction and other devices are employed to assist 
gravity. The average speed of drainage is about 12 
inches per hour, which can be increased mechanically 
by means of vacuum-pumps. To assist drainage per¬ 
colation vats are made of large diameter rather than 
deep, and are sloped from the outer circumference 


GENERAL INFORMATION ON CYANIDING. 189 

% 

towards the centre, although this slope is not very 
important if filter bottoms are properly constructed to 
allow the solutions to circulate freely under them. 

The character of the ore will determine the degree 
of fineness in crushing. An open porous ore might be 
crushed to the size of a pea, while a compact ore with 
metal disseminated through it in grains may need to 
pass a 60-mesh or finer screen. If the metal is in 
porous or loose ore in the form of seams or streaks, 
coarse crushing will answer. 

It is often necessary with refractory ores to use a 
preliminary treatment of lime to neutralize the acid 
salts which usually are found in partially oxidized 
pyritous ores, that are more or less dissoluble in 
water. Attempts have been made to neutralize these 
ores in the process of stamping by adding lime to the 
stamp-water. The objection to this proceeding is that 
a great degree of uncertainty must prevail as to the 
amount of lime required; and moreover, as the lime 
must be leached out of the ore by water later on, not 
much is to be gained, but considerable annoyance 
will be caused if too much lime finds its way into the 
ore. 

Mr. A. B. Paul used a cyanide solution in the 
stamp-battery, the object being to take up gold as it 
was liberated from the ore, thus hastening the opera¬ 
tion and lessening the amount of water waste. 


190 


CYANIDE PROCESSES . 


I here are several objections to this practice which 
make it unadvisable. 

A loss of cyanide takes place with such practice, 
and as cyanide cannot dissolve the coarse gold, noth¬ 
ing is to be gained. Cyanide will act on mercury, but 
not on gold covered with mercury, hence its use in the 
mortar might have a tendency to prevent the mercury 
from keeping up to its work. According to one authority 
mercury is not dissolved or acted upon by potassium 
\ an ' c le, but practice has proven otherwise, for at 
Mercur, where there is cinnabar in the ore, mercury is 
found m the slimes from the precipitation-box. Mer¬ 
cia > has also been found in the slimes where tailings 
from amalgamation have been cyanided, as at the 
Waihi Mine, New Zealand. * The ore in this latter 

instance is said to be practically free of base-metal 
sulphides. 

Conclusions for all Methods.-It is not claimed by 
any one, probably, that all ores can be treated suc¬ 
cessfully by cyaniding, for such is not the case; but 
the process can treat any ore where as much care is 

taken with ox.dation as in other processes and with 
equally good results. 

There may be given as one reason why better 
results have not been obtained in the treatment of tail- 


* A. Wilson. 






GENERAL INFORMATION ON CYAN I DING. 19 1 

ings that amalgam on the surface of gold protects it to 
an enormous extent from the solvent action of potas¬ 
sium cyanide. 

Another reason for bad results may be given, that 
not enough oxygen from the air was allowed to come 
in direct contact with the ore and solution. 

The poor results obtained in the treatment of con¬ 
centrates may be obviated by allowing more time for 
the cyanide solution to act upon them, or by finer 
pulverization. In both cases the action of the cyanide 
solution can be hastened by agitation. 

Advantages of Cyaniding.— 1 . The plant required is 
comparatively inexpensive. 

2. The extraction is arrived at without any previous 
ore treatment, except ordinary crushing, which must 
take place for every treatment. 

3. The extraction is simple and quite complete; 
tailings can be treated successfully when failure has 
attended other processes. 

4. The precious metals can be precipitated from the 
solution in various ways to suit the ideas of the 
operator, but the simplest way is by the electrical cur¬ 
rent with mercury cathode. 

5. The simple cyanide process extracts only the fine 
gold, thus necessitating previous amalgamation with 
free milling, and longer contact with the solution, and 
very fine crushing with refractory ore. The electrical 


CYANIDE PROCESSES. 


192 

method with mercury requires no previous amalgama¬ 
tion. 

6. The cost of treatment is not so high as to deter 
tire use of either process, and at times is quite reason¬ 
able, depending upon circumstances. 

7 ' The factor time enters into competition with 
machinery on the one hand, while machinery enters 
into competition with time on the other. An im¬ 
portant factor in favor of agitation is that the tanks 
can be cleared more readily for another operation; 

" lth perColation the y must be shoveled or sluiced out. 

8 ' TaIcose and clayey ores, such as make leaching 
difficult even when mixed with sand, are readily 
treated by agitation and the electric process. 

9- Failure to obtain satisfactory results has occurred 

from neglect on the part of the operator to properly 
neutrahze the ore before applying the cyanide solution. 

Failure has occurred in other instances because suffi¬ 
cient knowledge of the process was not possessed by 
t e operator. Early experiments proved very unsatis¬ 
factory, especially in the South Atlantic States, where 
this process seems to have been tested before it had 
attained its present state of perfection, or rather before 
tie intelligence now possessed upon the subject had 
been acquired by experiment. 

Cyanide of Potassium.-The cost of cyanide 98 per 
cent pure is fifty cents per pound in New York City. 


GENERAL INFORMATION ON CYANIDING. 193 

It is costly and worth economizing. Since the process 

has increased the demand for cyanide of potassium, it 

is of importance to buy it from some firm that can be 

relied upon, and that test it occasionally to ascertain 

its strength. The tendency, as the subject has been 

practically worked, is to greatly reduce the amount of 

cyanide used; where it was formerly customary to use 

1 i and more per cent of cyanide in the solution, 

equally good results are now obtained with a anc ] 

^ 10 

per cent solutions. There are two methods of ex¬ 
pressing strength of solutions which will be confusing 
unless understood. 1 pound KCN in 100 pounds of 
water is a 1 per cent solution; 10 pounds KCN in 
1000 pounds of water makes a 1 per cent solution; 
20 pounds KCN in 200 pounds of water is a 1 per 
cent solution. Another method of expressing the 
percentage of strength of solutions is to calculate their 
weight. For instance, 1 cubic foot of water weighs 
62 i pounds; hence 62J pounds KCN in 100 cubic feet 
of water would make a 1 per cent solution. As there 
are 32 cubic feet in 1 ton of water, the percentage is 
found by the proportion 

100 cu. ft. : 32 cu. ft. :: 62.5 lbs. : 20 lbs. 

That is, 20 pounds of cyanide to 2000 pounds of water 
is a 1 per cent solution. 


194 


CYANIDE PROCESSES. 


Pertaining to Hydrometallurgy.— i U. S. gallon of 
water measures 231 cubic inches and weighs 8.33 
pounds. 

1 cubic foot of water measures 1728 cubic inches 
and weighs 62.5 pounds, approximately. 

32 cubic feet of water weigh one ton of 2000 
pounds. 

21 cubic feet of pulverized ore make 1 ton. 

12 cubic feet of solid quartz rock make 1 ton,—this 
of course depending upon the specific gravity of the 
rock quartz, which is 2.6. 

1 fluid ounce is T *g of a pint. 

1 pint of water weighs approximately 1 pound avoir¬ 
dupois. 

24 grains make I pennyweight Troy. 

20 pennyweights make 1 ounce “ 

12 ounces make 1 pound “ 

1 pound Troy weighs 5760 grains avoirdupois. 

1 pound avoirdupois weighs 7000 grains Troy. 

I avoirdupois ton weighs 32,000 ounces. 

1 avoirdupois ton weighs 29,166 Troy ounces. 

1 assay ton weighs 29,166 + milligrams; hence 
every milligram of gold or silver in an assay represents 
ounces in the ton. 

1 assay ton weighs 29,166 -f grains; hence every 
grain of gold or silver extracted from this amount 
represents ounces of gold or silver in a ton of ore. 


1 95 


GENERAL INFORMATION ON CYANIDING. 

i gram weighs 15*432 grains. 

1 grain weighs .0648 gram. 

Area of circle is the diameter squared, and this mul¬ 
tiplied by the depth taken in the same multiple will 
give the cubic contents of a tank. If taken in inches, 
the answer will be in cubic inches; if taken in feet, the 
answer will be in cubic feet. 

Circumference of a circle is the diameter multiplied 
by 3.1416. 

Each cyanide vat should contain one day’s ore. If 
the operation requires six days, there should be six 

vats. If each vat contains 50 tons of ore, it is a 50-ton 
daily plant. 







INDEX. 


Acid, cyanhydric. 

Acid ores. . 

Acid, sulphuric, treatment of slimes. 

Acidity in ores. 

Agitation. 

“ processes. 

“ of slimes. 

‘‘ tests. 

Alkaline sulphides. . 

Alternating currents. 

Aluminum. 

Amalgamation. 

Ampere.... 

Ampere-hours... 

Anions. 

Anodes, 139; platinum, 165; carbon, 165; iron, 168; zinc 

Antimony. 

Arsenical ores. 

Assay, Crosse’s method. 

Assay of solution for gold and silver. 

Auriferous sulphurets. 


PAGE 

. . 28 

.8, 28 
.. 115 
•• 38 

18, 74 

132 
*• 132 
40, 72 

10 

•• i 3 6 
98 


. 142 

• 143 

• 139 
. 167 

9 > 3 6 

11 

52 

5 i 

125 


Base-metal ores. 


“ salts . 


.. ^ w 

Battery plates. . *. o 

Bismuth. 

Bottom discharge-valve. 

Bosqui, F. L. .. 



197 






























198 


INDEX. 


PAGE 

Bromide. 19 

Bullion from cyaniding. 119 

Butters’ pulp-distributor. 65 

Calculation of wires. 162 

Carbonate of copper. 9 

Carbon anodes. 165 

“ dioxide. 31 

Cathode. 170 

Cause of non-extraction. 36 

Caustic lime . 77 

“ potash. ,.27,98 

“ soda. 77 

Charcoal. 32 

“ precipitation. 87 

Charging vats. 63 

Chemical deductions. 25 

“ effects. 100 

“ processes. 26 

Chemicals for oxidation. 19 

Chemistry of the operation... . 25 

Chloride of silver.6, 85 

Chlorination process. 12 

Chlorine water... 21 

Christy’s experiments. 20 

Coarse crushing. , 6 

Cobalt. 12 

Commercial cyanide. 43 

Concentrates.3, 33 ? 126 

Conductivity of solutions. 138 

Copper-plate cathodes..«. 172 

Copper ores.9 ( 10 

“ sulphate. 34 

“ in zinc-boxes. 101 

Cost of electrocyaniding. X63 

“ “ cyanide plant. 7x 

Crookes, Wm. x^7 

Crosse’s gold assay for gold. 32 

Crushing, dry. 6 

Cuprous salt precipitation. 89 









































INDEX. 


199 


Current and molecular weight. 

Current. 

Current strength. 

Cyanicides. 

Cyanide consumption. 

‘ £ tests for. 

“ determination 

“ extraction. 

“ plant. 

“ process, scope of. 

Cyanogen and oxygen. 

Cyanogen bromide. 

Cyanide solutions, assay of. 

“ making up. 

“ “ stock.. 

“ “ strong.. 

“ “ tests. 


PAGE 

. 141 

. 160 

. 142 

. 28 

.3 2 > 39 

.39- 5 2 

33, 39, 5 2 > 53 
. 40 

. 55 

.34, 53 

. 22 

. 19 

. 5 i 

. 43 

. 44 

. 45 

. 5 2 


Decantation of slimes. 

Dehydrating roast. 

Determination of acidity. 

“ “ consumption. 

“ “ cyanide. 

u a ferri-cyanide. 

“ “ ferro- “ . 

“ “ free potassium cyanide 

“ “ free hydrocyanic acid. 

“ “ non-extraction. 

Dilute solutions. 

Discharge-valves.. 

Drainage. 

Dry crushing. 


. 129 

.. 12 

. 38 

. 33 

. 49 

. 5° 

. 50 

. 45 

. 48 

. 36 

.. . .16, 78 
. 61 

. 7 

6, 71, 128 


Electrical horse-power. 

“ precipitation. 

Electricity and oxygen. 

Electrocyaniding. 

“ cost of.. 

“ objections to 

Electrodes. 


... 144 
... 141 
... 146 

I 35> 145 
... 163 
... 164 
... 151 








































200 


INDEX. 


PAGE 

Electrolysis. 138 

Electrolyte. 146 

Eisner’s equation.14, 27 

Energy of current. 141 

Evaporation. 28 

Extraction.17, 23, 40 

“ determination of.36-40 

Ferri-cyanide. 30 

“ tests for. 30 

Ferri oxide. 30 

Ferro-cyanide. 30, 50 

“ test for. 30 

Ferrous oxide. 29 

Ferrous sulphate. 33 

Filling vats. 63 

Fine ore.37 

“ “ values in. a 

Filter bottoms. 6o 

“ P^ss. I3I 

“ press, slime treatment. 13! 

“ tanks. !23 

“ vacuum. .70, I2 3 

Fitness of ores for cyaniding. 7 

Float gold. ^ 

Flow of electricity. 142 

“ through electric precipitation-boxes. ^5 

“ through zinc “ “ ... gg 

Flux for gold precipitates. jjg 

Free hydrocyanic acid test. 

Free-milling ores. x 

Galena. IO 

Gas-coke. 

Gilmour-Young process. J32 

Gold, coarse. 6 

“ float. ^ 

* * fl ux 

UUA . 119 

* ‘ free-milling. - 

“ precipitates.u8 









































INDEX. 


201 


Gold, refractory. 

“ slime treatment 

“ solution. 

Graphite. 


PAGE 

... 2 

108, hi, 115, 119 

. 99 

•. 133 


Hanney’s experiments.16, 135 

Hydrogen peroxide. 19 


Impurities in solutions..4, 99 

Injectors. 68 

Intermediate filling. 65 

Iodine. 21 

Iodide of silver. 52 

Ions. 139 

Iron anodes. 168 

“ sulphate.28, 33 

“ sulphides. 28 

“ tanks. 3 1 

Laboratory samples.. 4 ° 

“ tests. 38 

Lathe for cutting zinc shavings. 97 

Leaching. . 74 > 7 6 

“ vats. 57 

Lead acetate. 100 

“ cathodes. I 74 

“ in zinc. 100 

Launders. 69 

Lime. 75 

Location of plants. 5 ^ 


MacArthur-Forrest patents 

Magnesia. 

Making up solutions. 

Manganese. 

McLauren’s experiments... 
Melting precipitates. 


28, 53, 75 
. 12 


15 
12 

41 

12 

16 
118 


Neutralizers 
Nickel. 





































202 


INDEX. 


Objections to zinc precipitation 

Ohm.. 

Ores, acid. 

“ antimony. 

‘ ‘ arsenic. 

“ base metal. 

“ concentrates, copper. 

“ discharging. 

u fineness of. 

“ free-milling. 

“ lead. 

11 Manganese.. 

‘ ‘ porous. 

‘ ‘ refractory. 

“ roasting. 

“ screening. 

“ slimes. 

“ suitable for process. 

“ sulphides. 

“ sulphurets. 

‘ ‘ refractory. 

“ roasting. 

“ tailings. 

“ tellurium. 

“ zinc. 

Oxygen and cyanide. 

Oxidation, chemicals for. 

Paracyanogen. 

Patents. 

Pelatan-Clerici cathode. 

“ “ process. 

Percentage of extraction. 

Percolation tests. 

Peroxide, barium. 

“ hydrogen. 

“ lead. 

“ manganese. 

‘ ‘ sodium. 

Pickling zinc. 


PAGE 
... IOI 

... 144 
... 8 

• * 9 > 3 6 

11 

... 8 
. .9, 10 
.. 61 

•• 7 

1 

12 
12 

• • 7 

.. 2 

.. 12 

•• 5 

.. 4 

• J > 13 

10, 28 
.. 125 
2 

12, 83 

• 3 
”, 23 

. 10 

• 15 

. 19 

. 22 

• i 5 

• 183 

• 175 

. 40 

. 41 

. 19 

• 19 

. 19 

19 
19 
100 









































INDEX. 


203 


PAGE 

Pipes. 69 

Plant . 55 , 70 

Platinum anodes. 165 

Pneumatic cyanide process. 133 

Porous ores. 7 

Potassium amalgam. 87 

“ bichromate. 19 

“ chlorate. 19 

“ cyanide. 41 

“ hydrate. 27 

“ nitrate. 19 

“ sulphate. 75 

“ sulphide.11, 75 

“ zinc cyanide.49, 95 

Preliminary washing. 75 

Precipitating-boxes, electrical. 176 

“ “ zinc. 68 

Precipitating by charcoal. 87 

“ by copper salts. 89 

“ by electricity.176, 183 

“ gold.86, 114 

“ potassium amalgam. 87 

“ by sodium amalgam. 86 

“ zinc.94, 96 

“ zinc fume. 114 

Process described. 53 

li electro-cyanide. 145 

“ Gilmour-Young. 132 

“ Hanney's. 16 

“ MacArthur-Forrest. 15 

“ Pelatan-Clerici. 178 

“ Siemens-Halske. 1 75 

“ Rae’s.-. 136 

Preliminary treatment. 77 

“ washing.36, 77 

Pyrites. 

Reaction pulp-distributor. 65 

Recovery of gold. r 5 2 

Refractory ores. 2 









































204 


INDEX. 


Roast, calcining...., 
u chloridizing. , 

“ dead . 

“ dehydrating . 
u oxidizing 
Roasting precipitates 

“ ores. 

“ silver. 

“ tellurides .. 

Roll crushing. 


PAGE 

12 

12 

.. 84 
12, 83 
12, 84 
• n 7 
12, 83 
. 84 
11 
6 


Scope of process. 

Schiedel, A. 

Screening. 

Settling-boxes. 

Settling-tanks. 

Side discharge-valves.. 
Siemens-Halske process 

Silver chloride. 

‘ ‘ deposition. 

“ extraction. 

“ iodide test. 

“ nitrate solutions.. 

Size of anodes. 

u “ cathodes. 

“ “ leaching-vats. .. 

Sizing. 

Slimes. 

“ decantation of.. 

Slime treatment. 

“ values.. 

‘ ‘ water for. .. _ 

Sluicing tailings. 

Specifications for plant., 

Soaking ore. 

Sodium amalgam. 

“ chloride.. 

“ hydrate. 

“ peroxide. 

Solutions, KCN. 


13, 26 
. 126 

• 5 

. 129 

4 

. 61 


. 175 

. 6 

. 85 

. 84 

. 52 

. 47 , 53 

. 161 

161, 173, 176 

. 57 

. 5 

. 4 

. 129 

no. 128, 131 

. 4 

. 131 

. 7 o 

. 7 i 

.64, 76 

. 86 

....159, 179 

. 49 

. 19 

. 44 








































INDEX. 


2 °5 


Solutions for leaching. 

“ weak. 

Stamping, dry. 

Standardizing solutions. 

Standardizing silver nitrate solutions... 

Standard solutions. 

Stock solutions. 

Strong solutions. 

Storage tanks. 

Sulphate of zinc. 

Sulphides .. 

Sulphurets. 

Sulphuric acid. 

“ “ treatment of gold slimes 

Suluman, H. L. 


l'AGE 


. 43 

. 45 

. 6 

... .44, 52 
....46, 53 

. 44 

. 44 

. 44 

.... 44, 70 

. 122 

.. .22, 125 

. I2 5 

28, 35> 90 

. 120 

. 116 


Tailings.. 

“ treatment. 

Tank, Pelatan-Clerici.... 
Tanks, gold solution . ... 

“ vacuum filter. 

Tellurides. 

Test for alkalies. 

“ “ cyanide. 

“ “ free acid. 

11 “ gold. 

“ u silver. 

Testing with silver nitrate 

Time factor. 

Time of drainage. 

“ “ leaching. 

Titration. 

Treatment of bullion. 


•’ 3 * 55 
... 121 
... 178 
.. 70 

68, 123 
.11, 23 

77 

• 52 , 53 
... 48 
•• 5i 
•• 5i 

•• 53 

.. 81 

.. 82 

.. Si 

• 47 , 53 

.. 113 


Vacuum filter.. 
“ pump.. 

Vats. 

Vat capacity... 
“ construction 
“ filling. 


... 68 
69, 123 

•• 59 

... 58 

.. 56 

•• 6 3 








































206 


INDEX . 


PAGE 

Vat foundations. 66 

“ steel... 31 

“ wooden... 39 

Voltage.143, 161 

Washing ore. 77 

Water, decomposition. 142 

“ for leaching. 65 

“ “ slimes. 66 

Watt. 144 

Wires, calculation of.. 162 

Zinc. I03 

“ amalgam. 94 

“ and lead. IO o 

“ anodes. ^7 

“ and strong solutions. 94 

“ blende. IO 

“ box . 68,108 

“ box slimes. 67 

“ consumption. IOI 

“ cost of.. io ^ 

“ fume precipitation. U4 

“ lathe. 97 

“ objections to . 99 

“ oxide . IOO 

zinc-potassic cyanide. 27 

“ precipitation.65, 94 

* l “ advantages. IOI 

“ “ hindrances to. IOO 

“ “ objections to. IOI 

“ shavings. g6 

“ sulphate. I22 














































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London: CHAPMAN & HALL, Limited. 
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“ Skeleton Construction in Buildings.8vo, 3 00 

Briggs’s Modern American School Buildings..-8vo, 4 00’ 

Carpenter’s Heating and Ventilating of Buildings.8vo, 3 00' 

Freitag’s Architectural Engineering.8vo, 3 50 

“ Fireproofing of Steel Buildings.8vo, 2 50 

Gerhard’s Guide to Sanitary House-inspection.16mo, 1 00 

“ Theatre Fires and Panics.12mo, 1 50 

Hatfield’s American House Carpenter.8vo, 5 00 

Holly’s Carpenters’ and Joiners’ Handbook.18mo, 75 

Kidder’s Architect’s and Builder’s Pocket-book..16mo, morocco, 4 00 

Merrill’s Stones for Building and Decoration.8vo, 5 00- 

1 

























Monckton’s Stair-building. 4to 

Patton’s Practical Treatise on Foundations.8vo, 

Siebert and Biggin’s Modern Stone-cutting and Masonry. .8vo,* 

Wait’s Engineering and Architectural Jurisprudence.8vo, 

Sheep, 

Law of Operations Preliminary to Construction in En¬ 
gineering and Architecture.8vo, 

Sheep, 

Law of Contracts.. 

Woodbury’s Fire Protection of Mills.g vo ’ 

Worcester and Atkinson’s Small Hospitals, Establishment and 
Maintenance, and Suggestions for Hospital Architecture, 

with Plans for a Small Hospital.12mo, 

The World’s Columbian Exposition of 1893.Large 4to, 


<< 


a 


4 00 

5 00 

1 50 

6 00 
6 50 

5 00 
5 50 
3 00 

2 50 


1 25 
1 00 


* 


ARMY AND NAVY. 

Bemadou’s Smokeless Powder, Nitro-cellulose, and the Theory 

of the Cellulose Molecule.12mo, 2 50 

* Bruff’s Text-book of Ordnance and Gunnery.8vo, 6 00 

Chase’s Screw Propellers and Marine Propulsion.8vo, 3 00 

Craig’s Azimuth.4to* 3 50 

Crehore and Squire’s Polarizing Photo-chronograph.8vo, 3 00 

Cronkhite’s Gunnery for Non-commissioned Officers..24mo, mar., 2 00 

* Davis’s Elements of Law.8vo, 2 50 

Treatise on the Military Law of United States. ..8vo, 7 00 

Sheep, 7 50 

De Brack s Cavalry Outpost Duties. (Carr.)... .24mo, morocco, 2 00 

Dietzs Soldiers First Aid Handbook.16mo, morocco, 1 25 

Dredge’s Modern French Artillery.4to, half morocco, 15 00 

Durand’s Resistance and Propulsion of Ships.8vo, 5 00 

*Dyer’s Handbook of Light Artillery.12mo, 3 00 

EissleFs Modern High Explosives.8vo, 4 00 

* Fiebeger’s Text-book on Field Fortification.Small 8vo, 2 00 

•Hoff’s Elementary Naval Tactics.8vo, 1 50 

Ingalls’s Handbook of Problems in Direct Fire.8vo, 4 00 

* “ Ballistic Tables.g vo ^ i gQ 

Lyons’s Treatise on Electromagnetic Phenomena.8vo, 6 00 

•Mahan’s Permanent Fortifications. (Mercur’s.).8vo, half mor. 7 50 

Manual for Courts-martial.16mo, morocco, 1 50 

•Mercur’s Attack of Fortified Places.12mo, 2 00 

Elements of the Art of War.gvo, 4 00 

Metcalfe s Cost of Manufactures—And the Administration of 

Workshops, Public and Private.8vo, 5 00 

Ordnance and Gunnery.12mo, 5 00 

Murray’s Infantry Drill Regulations.18mo, paper, 10 

•Phelps’s Practical Marine Surveying.g VOj 2 50 

Powell’s Army Officer’s Examiner.12mo, 4 00 

2 


































Sharpe’s Art of Subsisting Armies in War.18mo, morocco, 1 50 

Walke’s Lectures on Explosives. g vo 4 qq 

-Wheeler’s Siege Operations and Military Mining. 8 vo,' 2 00 

Vinthrop’s Abridgment of Military Law. 12 mo, 2 50 

Woodhull’s Notes on Military Hygiene.16mo, 1 50 

Young’s Simple Elements of Navigation.16mo, morocco, 1 00 

Second Edition, Enlarged and Revised.16mo, mor., 2 00 

ASSAYING. 

Fletcher s Practical Instructions in Quantitative Assaying with 

the Blowpipe. 12 mo, morocco, 1 50 

Furman’s Manual of Practical Assaying. 8 vo, 3 00 

Miller’s Manual of Assaying. 12 mo 1 00 

O’Driscoll’s Notes on the Treatment of Gold Ores. 8 vo[ 2 00 

Ricketts and Miller’s Notes on Assaying. 8 vo, 3 00 

Wilson’s Cyanide Processes.12mo, 1 50 

Chlorination Process . 12 mo, 1 60 

ASTRONOMY. 

Craig’s Azimuth.4to, 3 50 

Doolittle’s Treatise on Practical Astronomy. 8 vo, 4 00 

Gore’s Elements of Geodesy. 8 vo, 2 50 

Hayford’s Text-book of Geodetic Astronomy. 8 vo, 3 00 

Merriman’s Elements of Precise Surveying and Geodesy... . 8 vo, 2 50 

* Michie and Harlow’s Practical Astronomy. 8 vo, 3 00 


* White’s Elements of Theoretical and Descriptive Astronomy. 

12 mo, 2 00 

BOTANY. 

Baldwin’s Orchids of New England.Small 8 vo, 1 50 

Davenport’s Statistical Methods, with Special Reference to Bio¬ 
logical Variation.16mo, morocco, 1 25 

Thome and Bennett’s Structural and Physiological Botany. 

16mo, 2 25 

Westermaier’s Compendium of General Botany. (Schneider.) 8 vo, 2 00 

CHEMISTRY. 

Adriance’s Laboratory Calculations and Specific Gravity Tables, 

12mo, 1 25 

Allen’s Tables for Iron Analysis. 8 vo, 3 00 

Arnold’s Compendium of Chemistry. (Mandel.) (In preparation.) 

Austen’s Notes for Chemical Students.12mo, 1 50 

Bernadou’s Smokeless Powder.—Nitro-cellulose, and Theory of 

the Cellulose Molecule.12mo, 2 50 

Bolton’s Quantitative Analysis. 8 vo, 1 50 

Brush and Penfield’s Manual of Determinative Mineralogy.. 8 vo, 4 00 
Classen’s Quantitative Chemical Analysis by Electrolysis. (Her¬ 
rick—Boltwood.) . 8 vo, 3 00 


3 




























Cohn’s Indicators and Test-papers. 12mo o 

Craft^Short Course in Qualitative Chemical Analysis! '(Schaef-' 

Drechsel’s Chemical Reactions. (Merrill.). \ 95 

Rissler’s Modern High Explosives. ' " 8vo ’ 4 0Q 

“ EnZ rT eS , thdr AppHcations - (Prescott!) '(In preparation.) 
t nns n loduction to Chemical Preparations. (Dunlap.) 

Fletcher’s Practical Instructions in Quantitative Assaying 1 wTth 1 ^ 

~ n the , B ^ Wpi P e .; * * •..12mo, morocco, 1 50 

iuss Manual of Qualitative Chemical Analysis. (Wells.) 

« o j. - T 8vo, 5 00 

► ystem of Instruction in Quantitative Chemical 

Analysis. (Allen.) . fivn R 

Fuertes’s Water and Public Health.lo ’ , ~ 

Furman’s Manual of Practical Assaying.o’ « nn 

Gill’s Gas and Fuel Analysis for Engineers. ”i 2mo ’ 1 25 

Grotenfelt’s Principles of Modern Dairy Practice. (Woll.).. 12mo’ 2 00 

ammarsten’s Text-book of Physiological Chemistry. (Mandel.)’ 

Helm’s Principles of Mathematical Chemistry. (Morgan ) 12mo 1 50 
Holleman’s Text-book of Inorganic Chemistry. (Cooper.! 

Hopkins’s Oil-chemists’ Handbook. 

Keeps Cast Iron. (In preparation.) 

Ladd’s Manual of Quantitative Chemical Analysis.i 2mo 1 0 0 

Landauer s Spectrum Analysis. (Tingle.). o’ , 

t "m ar ^° hn S Practical Urinary Analysis. (Lorenz.) (in preparation 1 
Lob s Electrolysis and Electrosynthesis of Organic Compounds. ' 

Mandel’s Handbook for Bio-chemical Laboratory.'.'.I2Z’ ! 50 

Masons Water-supply. (Considered Principally from'a Sanb 

tary Standpoint.). o 

Examination of Water. (Chemical and Bacterio¬ 
logical.) . 

Meyer (Tingl t eT nati0n ° f Carbon Compounds! ' “ 

Miller’s Manual of Assaying. .)^ m °’ 1 00 

Mixter’s Elementary Text-book of Chemistry'!.,,”0 1 ™ 

Morgan’s Outline of Theory of Solution and its Results:!! l^, 1 00 

Elements of Physical Chemistry. 12mo 9 no 

Nmhols’s Water-supply. (Considered mainly from a Chemical’ 
and Sanitary Standpoint, 1883.)... ~ 0 

Laboratory Guide in Chemical Analyst !!.'!! ]' 8 vo’ 2 00 

O Driscoll s Lotes on the Treatment of Gold Ores.g vo ’ •> 00 

Ost and Kolbeck’s Text-book of Chemical Technology. (Lor-’ 
enz Bozart.) (In preparation.) 

4 

























* 1>eni ield's Notes on Determinative Mineralogy and Record of 

Mineral Tests.8vo, p a p eFj o 50 

Pinner s Introduction to Organic Chemistry. (Austen.)... 12mo, 1 50 
Poole’s Calorific Power of Fuels.8vo, 3 00 

* Reisig’s Guide to Piece-dyeing.8vo, 25 00 

Richards and Woodman’s Air, Water, and Food from a Sanitary 

Standpoint .8vo, 2 00 

Richards’s Cost of Living as Modified by Sanitary Science. 12mo, 1 00 

Cost of Food, a Study in Dietaries.12mo, 1 00 

Ricketts and Russell’s Skeleton Notes upon Inorganic Chem¬ 
istry. (Part I.—Nan-metallic Elements.). .8vo, morocco, 75 

Ricketts and Miller’s Notes on Assaying.8vo, 3 00 

Rideal s Sewage and the Bacterial Purification of Sewage. .8vo, 3 50 

Ruddiman’s Incompatibilities in Prescriptions.8vo, 2 00 

Schimpf’s Text-book of Volumetric Analysis.12mo, 2 50 

Spencer s Handbook for Chemists of Beet-sugar Houses. 

16mo, morocco, 3 00 

Handbook for Sugar Manufacturers and their Chem¬ 
ists .16mo, morocco, 2 00 


Stockbridge’s Rocks and Soils.8vo, 2 50 

* Tillman’s Elementary Lessons in Heat.8vo, 1 50 

Descriptive General Chemistry.8vo, 3 00 

Turneaure and Russell’s Public Water-supplies.8vo, 5 00 

Van Deventer’s Physical Chemistry for Beginners. (Boltwood.) 

12mo, 1 50 

W T alIce’s Lectures on Explosives.8vo, 4 00 


Wells’s Laboratory Guide in Qualitative Chemical Analysis. 


. .8vo, 

Short Course in Inorganic Qualitative Chemical Analy¬ 


sis for Engineering Students.12mo, 

Whipple’s Microscopy of Drinking-water.8vo, 

Wiechmann’s Sugar Analysis.Small 8vo, 

“ Lecture-notes on Theoretical Chemistry.... 12mo, 

Wilson’s Cyanide Processes.12mo, 

Chlorination Process.12mo, 

Wulling’s Elementary Course in Inorganic Pharmaceutical and 
Medical Chemistry.12mo, 


1 50 

1 50 
3 50 

2 50 

3 00 
1 50 

1 50 

2 00 


CIVIL ENGINEERING. 

BRIDGES AND ROOFS. HYDRAULICS. MATERIALS OF 
ENGINEERING. RAILWAY ENGINEERING. 


Baker’s Engineers’ Surveying Instruments.12mo, 3 00 

Bixby’s Graphical Computing Table... .Paper, 19^x241 inches. 25 

Davis’s Elevation and Stadia Tables.8vo, 1 00 

Folwell’s Sewerage. (Designing and Maintenance.).8vo, 3 00 

Freitag’s Architectural Engineering.8vo, 3 50 

5 


























Goodhue’s Municipal Improvements. ]2mo j 75 

Goodrich’s Economic Disposal ol Towns’ Refuse... . . . .V 8vo’ 3 50 
Gore’s Elements of Geodesy. 8vo ' 

Hayford’s Text-book of Geodetic Astronomy!!!!!!!!!!!!! ! 8 vo,' 


Howe’s Retaining-walls for Earth 


12mo 

Johnson’s Theory and Practice of Surveying.'.'.’.'.‘.'.‘.Small 8vo,’ 

Stadia and Earth-work Tables.8vo 

Kiersted’s Sewage Disposal. ^mo* 

Mahan’s Treatise on Civil Engineering. (1873.) (Wood.). 8vo 
Mahan’s Descriptive Geometry. 8vo ’ 

Memman’s Elements of Precise Surveying and Geodesy... ,8vo’ 
Merriman and Brooks’s Handbook for Surveyors.... 16mo, rnor., 

Merriman s Elements of Sanitary Engineering.8vo 

Nugents Plane Surveying. (In preparation.) 

Ogden’s Sewer Design. 12mo 

Patton’s Treatise on Civil Engineering.8vo, half leather! 7 50 

Reeds Topographical Drawing and Sketching. 4to 5 0 Q 

Rideal’s Sewage and the Bacterial Purification of Sewage. .8vo,’ 3 50 

!! Modern Stone-cutting and Masonry.. 8vo, 1 50 

Smiths Manual of Topographical Drawing. (McMillan.). .8vo, 2 50 
Trautwmes Civil Engineer’s Pocket-book.... 16mo, morocco, 

Waits Engineering and Architectural Jurisprudence. 8vo 


2 50 

3 00 
1 20 

4 00 
1 25- 
1 25 

5 00 

1 50 

2 50 
2 OO 
2 00 

2 00 


tt 


Law of Operations Preliminary to Construction in En¬ 
gineering and Architecture. 8vo 

Sheep, 


5 00 

6 00 
6 50 


Law of Contracts. 


8vo, 


5 00 
5 50 
3 00 
2 50 


Warren’s Stereotomy—Problems in Stone-cutting g vo ' 

Webb’s Problems in the Use and Adjustment of Engineering 

Instruments . ia ~ _ 

Wheeler s Elementary Course of Civil Engineering. 8 vo 4 00 
Wilson’s Topographic Surveying .. . g ; ]]][ 8vo ’ °° 


3 50 


BRIDGES AND ROOFS. 

Boiler s Practical Treatise on the Construction of Iron Highwav 
Bridges. & J 

* Boiler’s Thames River Bridge. !!!!!!!!! .*4to,‘ paplr! 5 OO 

Burrs Course on the Stresses in Bridges and Roof Trusses. 

Arched Ribs, and Suspension Bridges.8vo 3 50 

Du Bois’s Stresses in Framed Structures. Small 4to' 10 oo 

Foster’s Treatise on Wooden Trestle Bridges. .'.... 4to’ 5 00- 

Fowler’s Coffer-dam Process for Piers.... o' 9 ,- n 

Greene’s Roof Tosses.. 11!!!!!!!! [ ]' g™’ 1 25 

Bridge Trusses. 8yo ’ £ 5a 

Arches in Wood, Iron, and Stone. 8 vo’ 2 50 

Howe’s Treatise on Arches. 


G 
































Johnson, Bryan and Turneaure’s Theory and Practice in the 

Designing of Modern Framed Structures.Small 4to, 10 00 

Merriman and Jacoby’s Text-book on Roofs and Bridges: 

Part I—Stresses in Simple Trusses.8vo, 2 50 

Part II—Graphic Statics.8vo, 2 00 

Part III—Bridge Design. Fourth Ed. {In preparation.).. 8vo, 2 50 

Part IV.—Higher Structures.8vo, 2 50 

Morison’s Memphis Bridge.4to, 10 00 

Waddell’s De Pontibus, a Pocket Book for Bridge Engineers. 

16mo, mor., 3 00 

Specifications for Steel Bridges.12mo, 1 25 

Wood’s Treatise on the Theory of the Construction of Bridges 

and Roofs .8vo, 2 00 

Wright’s Designing of Draw-spans: 

Part I.—Plate-girder Draws.8vo, 2 50 

Part II.—Riveted-truss and Pin-connected Long-span Draws. 

8vo, 2 50 

Two parts in one volume.8vo, 3 50 


HYDRAULICS. 

Bazin’s Experiments upon the Contraction of the Liquid Vein 

Issuing from an Orifice. (Trautwine.).8vo, 

Bovey’s Treatise on Hydraulics.8vo, 

Church’s Mechanics of Engineering...8vo, 

Coffin’s Graphical Solution of Hydraulic Problems. .16mo, mor., 
Flather’s Dynamometers, and the Measurement of Power. 12mo, 

Folwell’s Water-supply Engineering.8vo, 

Frizell’s Water-power.8vo, 

Fuertes’s Water and Public Health.12mo, 

“ Water-filtration Works.12mo, 

Ganguillet and Kutter’s General Formula for the Uniform 
Flow of Water in Rivers and Other Channels. (Her- 

ing and Trautwine.).8vo, 

Hazen’s Filtration of Public Water-supply.8vo, 

Hazleurst’s Towers and Tanks for Water-works.8vo, 

Herschel’s 115 Experiments on the Carrying Capacity of Large, 

Riveted, Metal Conduits. 8vo, 

Mason’s Water-supply. (Considered Principally from a Sani¬ 
tary Standpoint.).8vo, 

Merriman’s Treatise on Hydraulics.8vo, 

* Michie’s Elements of Analytical Mechanics.8vo, 

Schuyler’s Reservoirs for Irrigation, Water-power, and Domestic 

Water-supply.Large 8vo, 

Turneaure and Russell. Public Water-supplies.8vo, 

Wegmann’s Design and Construction of Dams.4to, 

“ Water-supply of the City of New York from 1658 to 

1895 .•.4 to, 

Weisbach’s Hydraulics and Hydraulic Motors. (Du Bois.). .8vo, 

Wilson’s Manual of Irrigation Engineering.Small 8vo, 

Wolff’s Windmill as a Prime Mover.8vo, 

Wood’s Turbines.8vo, 

« Elements of Analytical Mechanics.8vo, 


MATERIALS OF ENGINEERING. 

Baker’s Treatise on Masonry Construction.8vo, 

Black’s United States Public Works.Oblong 4to, 

Bovey’s Strength of Materials arid Theory of Structures. .. .8vo, 

7 


2 00 

5 00 

6 00 

2 50 

3 00 

4 00 

5 00 

1 50 

2 50 


4 00 

3 00 

2 50 

2 00 

5 00 

4 00 

4 00 

5 00 
5 00 
5 00 

10 00 
5 00 
4 00 

3 00 

2 50 

3 OO 


5 00 
5 00 
7 50 



































Buri s Elasticity and Resistance of the Materials of Engineer- 

n > m fv-V.A.,..8vo, 5 00 

Byrnes Highway Construction.8vo, 5 00 

Inspection of the Materials and Workmanship Em- 

~ P lo 7 ed . in Construction.16mo, 3 00 

Church s Mechanics of Engineering.8vo, 6 00 

Du Bois’s Mechanics of Engineering. Vol. I.Smail 4to’ 10 00 

Johnsons Materials of Construction.Large 8vo 6 00 

Keep’s Cast Iron. {In preparation.) 

Lanza’s Applied Mechanics.8vo 7 50 

Martens s Handbook on Testing Materials. (Henning.).. 

Merrill’s Stones for Building and Decoration.'/.8vo* 5 00 

Merriman s Text-book on the Mechanics of Materials.8vo 4 00 

Mernman’s Strength of Materials.12mo 5 1 00 

Metcalf’s Steel. A Manual for Steel-users.12100* 2 00 

Patton’s Practical Treatise on Foundations. 8vo* 5 00 

RockAvell’s Roads and Pavements in France.V.’.12mo* 1 25 

Smiths Wire: Its Use and Manufacture. Small 4to* 3 00 

Spalding’s Hydraulic Cement.“ lamo! I 00 

•on. i , ^xt-book on Roads and Pavements.12mo 2 00 

Thursten’s Materials of Engineering.3 Parts, 8v o ; 8 00 

Pait I.—Ron-metallic Materials of Engineering and Metal- 

Part IL-Ironand' Stod.V.V.'.V.V7.7.'.7.7.': JV."'”':!' Ivo 1 S 
Part III. A Treatise on Brasses, Bronzes and Other AHoys* 

and Their Constituents. o v C. 9 c n 

Thurston’s Text-book of the Materials of Construction.''.!! Isvo! 5 00 

Tillsons Street Pavement 8 and Paving Materials. 8vo 4 00 

Waddell s De Pontibus. (A Pocket-book for Bridge Engineers./ ° 

Specifications for Steel Bridges. 12mn 1 ok 

Wood’s Treatise on the Resistance of Materials,’ and "an An- 

„ P endlx on the Preservation of Timber.8vo 2 00 

Elements of Analytical Mechanics.8vo* 3 00 


RAILWAY ENGINEERING. 

tw£. S t B u ldl ?^ S , and Structur es of American Railroads 4to 
3a f db00k of Railroad Location.. 16mo morocco; 

CranlllPs Tr±f t ‘ nee n 9 Fleld - book .16mo,’ morocco 

Crandall s Transition Curve .16mo, moroceo 

n , and 0ther Earthwork Tables.. 8vo 

Dawson s JJectnc Railways and Tramways.Small 4to, half mor.’, 
Engineering and Electric Traction Pocket-book. 

Dredge’s History of the Pennsylvania Railroad: ^^“.Paper 
rinkei s Tunneling, Explosive Compounds, and Rock Drills! 

Fisher’s Table of Cubic Yards. ^ 

Godwin’s Railroad Engineers’ Field-book and Explorers’^ G«S 

Howard’s Transition Curve Field-book V,'!,', 1 , 0 ’ nloro ««>, 

Hudson’s Tables for Calculating the Cubic Contents rf°Exca-’ 

vations STirl TilrriKQnL-monlo 

railway" Road-bed........ 7.7*7.'SvoJ 


5 

1 

2 

1 

1 


00 

50 

50 

50 

50 


12 50 


00 

00 


25 00 
25 



2 

1 

1 

3 

3 

2 


50 

50 

00 

00 

00 

00 




































Searles’s Field Engineering.16mo, morocco, 3 00 

“ Railroad Spiral.16mo, morocco, 1 50 

Taylor’s Prismoidal Formulae and Earthwork.8vo, 1 50 

* Trautwine's Method of Calculating the Cubic Contents of Ex¬ 
cavations and Embankments by the Aid of Dia¬ 
grams .8vo, 2 00 

The Field Practice of Laying Out Circular Curves 

for Railroads.12mo, morocco, 2 50 

Cross-section Sheet.Paper, 25 

Webb’s Railroad Construction.8vo, 4 00 


Wellington’3 Economic Theory of the Location of Railways.. 

Small 8vo, 5 00 


DRAWING. 


Barr’s Kinematics of Machinery.8vo, 

* Bartlett’s Mechanical Drawing.8vo, 

Durley’s Elementary Text-book of the Kinematics of Machines. 

(In preparation.) 

Hill’s Text-book on Shades and Shadows, and Perspective. .8vo, 
JoneB’s Machine Design: 

Part I.—Kinematics of Machinery.8vo, 

Part II.—Form, Strength and Proportions of Parts.8vo, 

MacCoTd’s Elements of Descriptive Geometry.8vo, 

“ Kinematics; or, Practical Mechanism.8vo, 

Mechanical Drawing.4to, 

Velocity Diagrams.8vo, 

* Mahan’s Descriptive Geometry and Stone-cutting.8vo, 

Mahan’s Industrial Drawing. (Thompson.).8vo, 

Reed’s Topographical Drawing and Sketching.4to, 

Reid’s Course in Mechanical Drawing.8vo, 

“ Text-book of Mechanical Drawing and Elementary Ma¬ 
chine Design.8vo, 

Robinson’s Principles of Mechanism.8vo, 

Smith’s Manual of Topographical Drawing. (McMillan.) .8vo, 
Warren’s Elements of Plane and Solid Free-hand Geometrical 

Drawing .12mo, 

“ Drafting Instruments and Operations.12mo, 

“ Manual of Elementary Projection Drawing.... 12mo, 
“ Manual of Elementary Problems in the Linear Per¬ 
spective of Form and Shadow.12mo, 

“ Plane Problems in Elementary Geometry.12mo, 

“ Primary Geometry.12mo, 

“ Elements of Descriptive Geometry, Shadows, and Per¬ 
spective .8 vo, 

“ General Problems of Shades and Shadows.8vo, 

“ Elements of Machine Construction and Drawing. .8vo, 
“ Problems, Theorems, and Examples in Descriptive 

Geometry.8vo, 

Weisbach’s Kinematics and the Power of Transmission. (Herr¬ 
mann and Klein.).8vo, 

Whelpley’s Practical Instruction in the Art of Letter. En¬ 
graving .12mo, 

Wilson’s Topographic Surveying.8vo, 

Wilson’s Free-hand Perspective.8vo, 

Woolf’s Elementary Course in Descriptive Geometry. .Large 8vo, 

9 


2 50 

3 00 


2 00 

1 50 
3 00 

3 00 
5 00 

4 00 
1 50 

1 50 
3 50 

5 00 

2 00 

3 00 
3 00 

2 50 

1 00 
1 25 
1 50 

1 00 

1 25 
75 

3 50 
3 00 
7 50 

2 50 
5 00 

2 00 

3 50 

2 50 

3 00 



































ELECTRICITY AND PHYSICS. 

Anthony and Brackett’s Text-book of Physics. (Magie.) 

A _ x . Small 8vo, 3 00 

Anthony s Lecture-notes on the Theory of Electrical Measur- 

ments .12mo, 1 00 

Benjamin’s History of Electricity. 8vo 3 00 

Benjamin’s Voltaic Cell.gvo’ 3 00 

Classen’s Qantitative Chemical Analysis by Electrolysis. Her¬ 
rick and Boltwood.).‘. g vo 3 qq 

Crelioie and Squier’s Polarizing Photo-chronograph.8vo, 3 00 

Dawson s Electric Railways and Tramways..Small 4to, half mor.. 12 50 
Dawsons Engineering ” and Electric Traction Pocket-book. 

> -n . 16mo, morocco, 4 00 

rvfiT’ xi 8 Eynamometers, and the Measurement of Power.. 12mo, 3 00 

Gilberts De Magnete. (Mottelay.). gvo 2 50 

Holman’s Precision of Measurements. !!!!!!.! 8vo’ 2 00 

Telescopic Mirror-scale Method, Adjustments, and 

Tests .... # . Tjsltsq 8vo 75 

Landauer’s Spectrum Analysis. (Tingle.*)*. V. V. VV...... 8vo’ 3 00 

Le Chatelier’s High-temperature Measurements. (Boudouard— 

Burgess.) . l^mo 3 00 

Lob’s Electrolysis and Eleetrosyntiiesis of Organic Compounds' 

(Lorenz.) . r 12mo' 1 00 

Treatise on Electromagnetic Phenomena. 8vo' 6 00 

MlCh L%htf IementS ° f WaVe Motion Relatin g to Sound and 
Niaudet’s^ Elementary Treatise on Electric Batteries' '(Fish- 4 °° 

Thn^w ai qf ^ obart ’ s Electric Generators..Smaii 4to, half mor.’ 10 00 
Ihurstons Stationary Steam-engines. o rh 

•Tillman. Elementary Lessons in Heat... 1.!!!.'!!!.'i;i jvo 1 50 
ory and Pitcher. Manual of Laboratory Physics. .Small 8vo' 2 OO 

._ . LAW. 

Davis. Elements of Law. 8 2 ^ 

* Treatise on the Military Law of United States..8vo’ 7 00 

Manual for Courts-martial in m Sheep, 7 50 

Wait’s Engineering and Architectural Jurisprudence! °Svo, 6 00 

La\v of Operations Preliminary to Construction i^En- 6 5(> 
gmeermg and Architecture. o vn nA 

“ Law of Contracts. Sh g e *P> f “ 

Winthrop’s Abridgment of Military Law. V.i2mo,’ 2 50 


MANUFACTURES. 

Beaumont’s Woollen and Worsted Cloth Manufacture.... 12mo 1 
Bernadou s Smokeless Powder—Nitro-cellulose and Theory of 

the Cellulose Molecule. .o,,.. 

Bolland’s Iron Founder. .iamn'iSf 

;; "The Iron Founder ” Suppiemen't*. *.’.'.'.'.!... ’. f 2 ^o 
Encyclopedia of Founding and Dictionary of Foundry 

Modera S ^ d w"^l-£? ctice of Moulding. .. . 12mo, 


50 

50 

50 

50 


Kssler’s Modern High'^5^7.7: -'' "Xo 4 m 

Fitzgeralds Z B™ e |on I, Maeh*in^st^' Cat * 0n3 , .^ reSC0 ^ 

10 





























Ford’s Boiler Making for Boiler Makers.I81110, 

Hopkins’s Oil-chemists’ Handbook.8vo, 

Keep’s Cast Iron. {In preparation.) 

Metcalf’s Steel. A Manual for Steel-users.12mo, 

Metcalf’s Cost of Manufactures—And the Administration of 

Workshops, Public and Private.8vo, 

Meyer’s Modern Locomotive Construction.4to, 

* Reisig’s Guide to Piece-dyeing.8vo, 

Smith’s Press-working of Metals.8vo, 

“ Wire: Its Use and Manufacture.Small 4to, 

Spalding’s Hydraulic Cement.12mo, 

Spencer’s Handbook for Chemists of Beet-sugar Houses. 

16mo, morocco, 

“ Handbook for Sugar Manufacturers and their Chem¬ 
ists.16mo, morocco, 

Thurston’s Manual of Steam-boilers, their Designs, Construc¬ 
tion and Operation.8vo, 

Walke’s Lectures on Explosives.8vo, 

West’s American Foundry Practice.12mo, 

“ Moulder’s Text-book.12mo, 

Wiechmann’s Sugar Analysis.Small 8vo, 

Wolff’s Windmill as a Prime Mover.8vo, 

Woodbury’s Fire Protection of Mills.8vo, 


1 00 
3 OO 

2 00 

5 00 
10 00 
25 00 


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2 


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2 

2 

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50 


MATHEMATICS. 


Baker’s Elliptic Functions.8vo, 

* Bass’s Elements of Differential Calculus.12mo, 

Briggs’s Elements of Plane Analytic Geometry.12mo, 

Chapman’s Elementary Course in Theory of Equations.. .12mo, 

Compton’s Manual of Logarithmic Computations.12mo, 

Davis’s Introduction to the Logic of Algebra.8vo, 

Halsted’s Elements of Geometry.8vo, 

“ Elementary Synthetic Geometry.8vo, 

Johnson’s Three-place Logarithmic Tables: Vest-pocket size, pap., 

100 copies for 

Mounted on heavy cardboard, 8 X 10 inches, 

10 copies for 

“ Elementary Treatise on the Integral Calculus. 

Small 8vo, 

“ Curve Tracing in Cartesian Co-ordinates.12mo, 

Treatise on Ordinary and Partial Differential 

Equations.Small 8vo, 

“ Theory of Errors and the Method of Least 
Squares .12mo, 

* “ Theoretical Mechanics.. „.. 12mo, 

•Ludlow and Bass. Elements of Trigonometry and Logarith¬ 
mic and Other Tables.8vo, 

« Trigonometry. Tables published separately. .Each, 

Merriman and Woodward. Higher Mathematics.8vo, 

Merriman’s Method of Least Squares. 8vo, 

Rice and Johnson’s Elementary Treatise on the Differential 

Calculus.Small 8vo, 

“ Differential and Integral Calculus. 2 vols. 

in one.Small 8vo, 

Wood’s Elements of Co-ordinate Geometry.8vo, 

« Trigometry: Analytical, Plane, and Spherical.... 12mo, 

11 


1 50 

4 OO 
1 00 

50 
50 
50 
1 75 

1 50 
15 

5 00 
25 

2 00 


1 50 
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3 50 

1 50 
3 OO 


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2 00 
1 25 
1 00 

1 50 
3 09 
5 00 


MECHANICAL ENGINEERING. 

materials of engineering, steam engines 

AND BOILERS. 

Baldwin's Steam Heating for Buildings. 12mo 2 50 

?, ^ ne “ atics of Machinery... ..V.’. m8vo * \ 50 

Bartlett s Mechanical Drawing. q vo ’ o 

Benjamin s Wrinkles and Recipes.V..i 2ni o 2 00 

Carpenters Experimental Engineering.7.77* 8vo 6 00 

Clerk’s Gas and OU Buildin S s .v ■ • ■■■ g "i 3 «> 

Cromwell’s Treatise on Toothed Gearing'.'.:.'.'.'.'.:.' " " 2 mo 1 50 

Burley’s Elementary Text-book of the Kinematics of Machines. 

I lather’s Dynamometer, and the Measurement of 3 00 

Si 1 , 1 ,’? G * s a " Fuel Analysis* for' Engineers.'.'.'.'mno 

Hall’s Car Lubrication. \Z mo > 

Jones’s Machine Design: -i^rao. 

Part I. Kinematics of Machinery. « 

n—Form, Strength and Proportions of Parts:8vo’ 

Kent s Mechanical Engineers’ Pocket-book.... 16mo, morocco’ 

Ma7corfTK| and P f °"' er {In Preparation 

MacCords Kinematics- or. Practical Mechanism. 8vo 5 00 

Mechanical Drawing. at®’ ? 

, , Velocity Diagrams...'. 400 

Mahan s Industrial Drawing. (Thompson.).gvo 

Poole s Calorific Power of Fuels.. F ; .o V0 ’ 

Reid’s Course in Mechanical Drawing. 77 .8vn’ 

^Machine Drawin S' aiid ' Elementary 

Richards’s Compressed Air . io°’ 

Robinson’s Principles of Mechanism'.’.’.'.'.’.. £°’ 

Smith s Press-working of Metals..;./. t ’ 

Thurston’s Treatise on Friction and Lost Work in Machin- 

,, ery and Mill Work. 8vo 

Animal as a Machine and Prime Motor’and the 
w Laws of Energetics... io , AA 

Warren’s Elements of Machine Construction 'and Drawing 8vo 7 ?n 
M eisbach s Kinematics and the Power of Transmission. g (Herr- ? 5 ° 

Machinery of Transmission and Governors. (Herr- 
mann—Klein.) . ' A 1 

w ? y( ?r, aulics ^raulic Motors.' ' (Du Boi's j 8vo 

Woiff s Windmill as a Prime Mover. ' 

Moods Turbines. . 

.. 

MATERIALS OF ENGINEERING. 

Bovej s Stiength of Materials and Theory of Structures 8vn 7 5n 
ing “y and Resistan<:e of the Materials of Engineer-’ 5 ° 

"Church’s Mechanics’ of*Engineering.? vo ’ 

JohnsoiTs Materials of Construction....'.'.’.’..‘Laiw'S 

Keep’s Cast Iron. (In preparation.) °’ 

Lanza s Applied Mechanics. a 

Martens’s Handbook on Testing Materials. (Henning.) 8vo’ 
-Mernman’a Text-book on the Mechanics of Materifu.'.'.' .'gvo 
Strength of Materials.7l2mo 


1 50 
3 50 
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2 00 

3 00 
1 50 
3 00 
3 00 

3 00 


5 00 
5 00 
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7 50 
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Metcalfs Steel. A Manual for Steel-users.12mo, 2 OO 1 

Smith’s Wire: Its Use and Manufacture.Small 4to, 3 00- 

Thurston’s Materials of Engineering.3 vols., 8vo, 8 OO 

Part II.—Iron and Steel.8vo, 3 50 

Part III.—A Treatise on Brasses, Bronzes and Other Alloys 

and their Constituents.8vo, 2 50 

Thurston’s Text-book of the Materials of Construction... .8vo, 5 00 
Wood’s Treatise on the Resistance of Materials and an Ap¬ 
pendix on the Preservation of Timber.8vo, 2 OO 

Elements of Analytical Mechanics.8vo, 3 00 


STEAM ENGINES AND BOILERS. 

Carnot’s Reflections on the Motive Power of Heat. (Thurston.) 

12mo, 1 50 

Dawson’s “ Engineering ” and Electric Traction Pocket-book. 

16mo, morocco, 4 00 

Ford’s Boiler Making for Boiler Makers.18mo, 1 00 

Hemenway’s Indicator Practice and Steam-engine Economy. 

12mo, 2 00 

Hutton’s Mechanical Engineering of Power Plants.8vo, 5 00 

Heat and Heat-engines.8vo, 5 00 

Kent’s Steam-boiler Economy.8vo, 4 00 

Kneass’s Practice and Theory of the Injector.8vo, 1 50 

MacCord’s Slide-valves.8vo, 2 00 

Meyer’s Modern Locomotive Construction.4to, 10 00 

Peabody’s Manual of the Steam-engine Indicator.12mo, 1 50 

Tables of the Properties of Saturated Steam and 

Other Vapors.8vo, 1 00 

Thermodynamics of the Steam-engine and Other 

Heat-engines.8vo, 5 00 

“ Valve-gears for Steam-engines.8vo, 2 50 

Peabody and Miller. Steam-boilers.8vo, 4 00 

Pray’s Twenty Years with the Indicator.Large 8vo, 2 50 

Pupin’s Thermodynamics of Reversible Cycles in Gases and 

Saturated Vapors. (Osterberg.).12mo, 1 25 

Reagan’s Locomotive Mechanism and Engineering.12mo, 2 00 

Rontgen’s Principles of Thermodynamics. (Du Bois.)... .8vo, 5 00 
Sinclair’s Locomotive Engine Running and Management. .12mo, 2 00 
Smart’s Handbook of Engineering Laboratory Practice. . 12mo, 2 50 

Snow’s Steam-boiler Practice.8vo, 3 00 

Spangler’s Valve-gears.8vo, 2 50 

“ Notes on Thermodynamics.12mo, 1 00 

Thurston’s Handy Tables.8vo, 1 50 

“ Manual of the Steam-engine. <....2 vols., 8vo, 10 00 

Part I.—History, Structure, and Theory.8vo, 6 00 

Part II.—Design, Construction, and Operation.8vo, 6 00 

Thurston’s Handbook of Engine and Boiler Trials, and the Use 


... . 8vo, 

5 00 


2 50 

l Prac- 



1 50 




Manual of Steam-boilers, Their Designs, Construc¬ 
tion, and Operation.8vo, 

Weisbach’s Heat, Steam, and Steam-engines. (Du Bois.)..8vo, 

Whitham’s Steam-engine Design.8vo, 

Wilson’s Treatise on Steam-boilers. (Flather.).16mo, 

Wood’s Thermodynamics, Heat Motors, and Refrigerating 
Machines .Bvo, 


00 

00 

00 

50 


4 00 


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MECHANICS AND MACHINERY. 

Barr’s Kinematics of Machinery.8vo, 

Bovey’s Strength of Materials and Theory of Structures. .8vo, 

Chordal.—Extracts from Letters.12mo, 

Church’s Mechanics of Engineering.8vo, 

Notes and Examples in Mechanics.8vo, 

Compton’s First Lessons in Metal-working.12mo, 

Compton and De Groodt. The Speed Lathe.12mo, 

Cromwell’s Treatise on Toothed Gearing.12ma, 

Treatise on Belts and Pulleys.12mo, 

Dana’s Text-book of Elementary Mechanics for the Use of 

Colleges and Schools.12mo, 

Dingey’s Machinery Pattern Making.12mo' 

Dredge’s Record of the Transportation Exhibits Building of the 

World’s Columbian Exposition of 1893.4to, half mor., 

Du Bois’s Elementary Principles of Mechanics: 

Vol. I.—Kinematics.8vo 

Vol. II.—Statics...gvo* 

Vol. III.—Kinetics.g v0 ’ 

Du Bois’s Mechanics of Engineering. Vol. I.Small 4to! 

Durley’s Elementary Text-book of the Kinematics of Machines! 

_ (In preparation.) 

Fitzgeralds Boston Machinist.lGmo, 

Flather’s Dynamometers, and the Measurement of Power. 12mo! 

TT J ^ Ro P e Drivin S.12mo, 

Halls Car Lubrication.12mo 

Holly’s Art of Saw Filing.18mo! 

* Johnson’s Theoretical Mechanics.12mo J 

Jones’s Machine Design: 

Part I—Kinematics of Machinery.8 V0 

Part II—Form, Strength and Proportions of Parts..!.8vo! 
Kerr’s Power and Power Transmission. (In preparation.) 

Lanza’s Applied Mechanics.g vo 

MacCord’s Kinematics; or, Practical Mechanism..!...!.,!8vo,’ 

“ Velocity Diagrams.! .8vo* 

Merriman’s Text-book on the Mechanics of Materials.8va* 

* Michie’s Elements of Analytical Mechanics.[. ,Svo, 

Reagan’s Locomotive Mechanism and Engineering. 

Reid’s Course in Mechanical Drawing.gyg’ 

Text-book of Mechanical Drawing and Elementary 

Machine Design. g v ^ 

Richards’s Compressed Air.V.V.lbmo* 

Robinson’s Principles of Mechanism. .8vo > 

Sinclair’s Locomotive-engine Running and Management 12mo’ 

Smith’s Press-working of Metals... . 8vo 

Thurston’s Treatise on Friction and Lost Work in Machin¬ 
ery and Mill Work.g VOj 

Animal as a Machine and Prime Motor, and the’ 

Laws of Energetics.12mo 

Warren’s Elements of Machine Construction and Drawing, .Svc/ 
Weisbach’s Kinematics and the Power of Transmission! 

(Herrman—Klein.) .g vo * 

Machinery of Transmission and Governors. (Herr- 

(man—Klein.) .g vo 

Wood’s Elements of Analytical Mechanics. !!...! 8vo > 

Principles of Elementary Mechanics. V. . . Vl&no 

" Turbines .' ’ g vo ’ 

The World’s Columbian Exposition of 1893.* 

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METALLURGY. 


Egleston’s Metallurgy of Silver, Gold, and Mercury: 

Vol. I—Silver.8vo, 7 50 

Vol. II.—Gold and Mercury.8vo, 7 50 

Keep’s Cast Iron. (In preparation.) 

Kunhardt’s Practice of Ore Dressing in Europe.8vo, 1 50 

Le Chatelier’s High-temperature Measurements. (Boudouard— 

Burgess.) .12mo, 3 00 

Metcalfs Steel. A Manual for Steel-users.12mo, 2 00 

Thurston’s Materials of Engineering. In Three Parts.8vo, 8 00 

Part II.—Iron and Steel.8vo, 3 50 

Part III.—A Treatise on Brasses, Bronzes and Other Alloys 

and Their Constituents.8vo, 2 50 


MINERALOGY. 

Barringer’s Description of Minerals of Commercial Value. 

Oblong, morocco, 2 50 

Boyd’s Resources of Southwest Virginia.8vo, 3 00 

“ Map of Southwest Virginia.Pocket-book form, 2 00 

Brush’s Manual of Determinative Mineralogy. (Penfield.) .8vo, 4 00 

Chester’s Catalogue of Minerals.8vo, paper, 1 00 

Cloth, 1 25 

“ Dictionary of the Names of Minerals.8vo, 3 50 

Dana’s System of Mineralogy.Large 8vo, half leather, 12 50 

“ First Appendix to Dana’s New “ System of Mineralogy.” 

Large 8vo, 1 00 

“ Text-book of Mineralogy.8vo, 4 00 

“ Minerals and How to Study Them.12mo, 1 50 

“ Catalogue of American Localities of Minerals. Large 8vo, 1 00 

“ Manual of Mineralogy and Petrography.12mo, 2 00 

Egleston’s Catalogue of Minerals and Synonyms.8vo, 2 50 

Hussak’s The Determination of Rock-forming Minerals. 

(Smith.) .Small 8vo, 2 00 

* Penfield’s Notes on Determinative Mineralogy and Record of 

Mineral Tests.8vo, paper, 50 

Rosenbuseh’s Microscopical Physiography of the Rock-making 

Minerals. (Idding’s.).8vo, 5 00 

* Tillman’s Text-book of Important Minerals and Rocks.. 8vo, 2 00 

Williams’s Manual of Lithology.8vo, 3 00 


MINING. 

Beard’s Ventilation of Mines. 12mo, 

Boyd’s Resources of Southwest Virginia.8vo, 

“ Map of Southwest Virginia.Pocket-book form, 

* Drinker’s Tunneling, Explosive Compounds, and Rock 

Drills.4to, half morocco, 

Eissler’s Modern High Explosives.8vo, 

Goodyear’s Coal-mines of the Western Coast of the United 

States .12mo, 

Ihlseng’s Manual of Mining.8vo, 

Kunhardt’s Practice of Ore Dressing in Europe.8vo, 

O’Driscoll’s Notes on the Treatment of Gold Ores.8vo, 

Sawyer’s Accidents in Mines.8vo, 

Walke’s Lectures on Explosives.8vo, 

Wilson’s Cyanide Processes. 

Wilson’s Chlorination Process.12mo, 


2 

3 

2 


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25 


5 00 

1 25 

2 00 


Wilson’s Hydraulic and Placer Mining.12mo, 2 00 

Wilson’s Treatise on Practical and Theoretical Mine Ventila¬ 
tion .12mo, 1 25 

SANITARY SCIENCE. 

Pol well’s Sewerage. (Designing, Construction and Maintenance.) 

8 vo, 3 00 

Water-supply Engineering. 8 vo, 4 00 

Fuertes’s Water and Public Health.12mo, 1 50 

“ Water-filtration Works. 12 mo’ 

Gerhard’s Guide to Sanitary House-inspection. 16010 ’ 

Goodrich’s Economical Disposal of Towns’ Refuse.. .Demy 8 vo, 

Hazen’s Filtration of Public Water-supplies. 8 vo, 

Kiersted’s Sewage Disposal.12mo’ 

Mason’s Water-supply. (Considered Principally from a San¬ 
itary Standpoint. 8 vo, 

Examination of Water. (Chemical and Bacterio- 

logical.) . 12 mo, 

Mernman s Elements of Sanitary Engineering. 8 vo, 

Nichols’s Water-supply. (Considered Mainly from a Chemical 

and Sanitary Standpoint.) (1883.) . 8 vo 2 50 

Ogden’s Sewer Design. ....'. 12 ^ 2 00 

Richards’s Cost of Food. A Study in Dietaries.12mo! 1 00 

Richards and Woodman’s Air, Water, and Food from a Sani¬ 
tary Standpoint.. 

Richards’s Cost of Living as Modified by Sanitary Science. 12mo,’ 

Rideal’s Sewage and Bacterial Purification of Sewage. 8 vo 

Turneaure and Russell’s Public Water-supplies. 8 vo’ 

Whipple’s Microscopy of Drinking-water. 8 vo’ 

Woodhull’s Notes on Military Hygiene.16mo’ 

MISCELLANEOUS. 

Barker’s Deep-sea Soundings. g vo 2 00 

Emmons’s Geological Guide-book of the Rocky Mountain Ex¬ 
cursion of the International Congress of Geologists. 

Ferrel’s Popular Treatise on the Winds. 8 vo 4 00 

Haines’s American Railway Management. * 12mo’ 2 50 

Mott’s Composition, Digestibility, and Nutritive Value of Food! 

« t-* 11 , .. Mounted chart, 

Fallacy of the Present Theory of Sound.16mo 

Ricketts’s History of Rensselaer Polytechnic Institute, 1824- 

—, ’ U'' y ‘.Small 8 vo, 

Rotherham s Emphasised New Testament.Large 8 vo, 

“ Critical Emphasised New Testament. 12mo’ 

Steel s Treatise on the Diseases of the Dog. gvo’ 

Totten’s Important Question in Metrology.. 8 vo’ 

The World’s Columbian Exposition of 1893.. . . . . . 4to’ 

Worcester and Atkinson. Small Hospitals, Establishment and 
Maintenance, and Suggestions for Hospital Architecture 
with Plans for a Small Hospital.12mo’ 

HEBREW AND CHALDEE TEXT-BOOKS. 

Greens Grammar of the Hebrew Language... 8 vo 

Elementary Hebrew Grammar.. .7. .’.’..i 2 mo ' 

“ Hebrew Chrestomathy. " gvo’ 

Gesenius’s Hebrew and Chaldee Lexicon to the ‘Old Testament 

t ++ Sci lptures. (Tregelles.).Small 4to, half morocco, 5 00 

Lettens’s Hebrew Bible. 8vo ’ 2 25 


2 00 
1 00 
3 50 
00 
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50 


1 25 

1 00 

3 00 

2 00 

1 50 
3 50 

2 50 
1 00 


1 25 


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2 00 


16 









































JUN “5 1902 

1COPVBSI. ** f *'V. 
JUN. 5 190? 


















































